two pointers

Longest Palindromic Substring

Find the longest contiguous palindromic substring in a given string using dynamic programming and two-pointer expansion …

Container With Most Water

Find two vertical lines that can form a container with the most water in a given array of heights.

3Sum

Given an integer array, return all unique triplets where the sum is zero using two-pointer scanning with careful duplica…

3Sum Closest

Find the sum of three integers in an array that is closest to a given target using two-pointer scanning.

4Sum

The 4Sum problem requires finding all unique quadruplets in an array that sum to a specific target value.

Remove Nth Node From End of List

Remove the nth node from the end of a linked list using a two-pointer approach to solve efficiently.

Remove Duplicates from Sorted Array

Learn how to remove duplicates from a sorted array in-place using two-pointer scanning while preserving element order.

Remove Element

Remove Element challenges you to remove a value from an array in-place using efficient two-pointer scanning and tracking…

Find the Index of the First Occurrence in a String

Locate the first occurrence of a substring within a string using a two-pointer scanning strategy and invariant tracking …

Next Permutation

Next Permutation is a medium-difficulty problem focusing on generating the next lexicographically greater permutation of…

Trapping Rain Water

Calculate the total trapped rain water using the elevation map array, leveraging dynamic programming and two-pointer pat…

Rotate List

Rotate a singly linked list to the right by k positions using careful pointer manipulation and two-pointer traversal tec…

Sort Colors

Sort Colors requires in-place reordering of an array using a two-pointer scanning strategy to group 0s, 1s, and 2s effic…

Remove Duplicates from Sorted Array II

Solve the problem of removing duplicates from a sorted array in-place, ensuring each element appears at most twice, usin…

Remove Duplicates from Sorted List II

Remove duplicates from a sorted linked list, leaving only distinct values, and return the modified list in sorted order.

Partition List

Partition a linked list such that all nodes less than x come before nodes greater than or equal to x while preserving re…

Merge Sorted Array

Merge two sorted arrays into the first array in non-decreasing order, using a two-pointer approach.

Valid Palindrome

Check if a given string is a valid palindrome by using two-pointer scanning and invariant tracking techniques.

Linked List Cycle

Determine if a given linked list contains a cycle using pointer manipulation or hashing, focusing on detecting repeated …

Linked List Cycle II

Identify the start of a cycle in a linked list using pointer manipulation, efficiently handling edge cases without modif…

Reorder List

Reorder List requires careful pointer manipulation in a singly linked list to interleave nodes from the ends without alt…

Sort List

Sort List requires sorting a singly linked list efficiently using pointer manipulation and merge sort for optimal perfor…

Reverse Words in a String

Reverse Words in a String requires reordering words using precise two-pointer scanning with careful space handling for e…

Intersection of Two Linked Lists

Given two linked lists, find the node where they intersect or return null if they do not.

Compare Version Numbers

Compare two version numbers by checking their individual revisions, considering missing revisions as zero, using a two-p…

Two Sum II - Input Array Is Sorted

Solve the Two Sum II problem efficiently using binary search over a valid answer space in a sorted array.

Rotate Array

Rotate Array challenges you to shift elements right by k steps using precise two-pointer scanning and invariant tracking…

Happy Number

Determine if a number is happy by repeatedly summing squares of digits using two-pointer scanning to detect cycles effic…

Palindrome Linked List

Solve Palindrome Linked List by finding the midpoint, reversing the second half, and comparing mirrored nodes in linear …

Move Zeroes

Move all zeros in an array to the end while preserving the order of non-zero elements using efficient in-place operation…

Find the Duplicate Number

The problem involves finding the duplicate number in an array of integers, using a binary search approach over the valid…

Find Median from Data Stream

Implement a MedianFinder class that supports adding numbers and finding the median from a data stream.

Create Maximum Number

Create Maximum Number involves merging digits from two arrays while preserving order, maximizing the resulting number.

Reverse String

Reverse a character array in-place using a two-pointer scanning technique, ensuring minimal memory and correct index swa…

Reverse Vowels of a String

Reverse Vowels of a String uses a two-pointer approach to reverse the vowels in a string while leaving the consonants in…

Intersection of Two Arrays

Find the intersection of two arrays while ensuring unique elements using efficient array scanning and hash lookups.

Intersection of Two Arrays II

Find the intersection of two arrays, accounting for multiple occurrences of the same number.

Is Subsequence

Determine if one string is a subsequence of another using state transition dynamic programming for accurate character ma…

String Compression

Compress a character array in-place by converting consecutive repeated characters into counts using two-pointer scanning…

Assign Cookies

Maximize content children by assigning at most one cookie per child using two-pointer scanning and greedy sorting techni…

Circular Array Loop

Detect whether a circular array contains a loop of consistent direction using efficient array scanning and hash lookup t…

Heaters

Determine the minimum heater radius to cover all houses using a binary search over potential radius values efficiently.

Magical String

Count the number of '1's in the first n characters of a magical string using two-pointer scanning and invariant tracking…

Longest Uncommon Subsequence II

Find the longest string in an array that is not a subsequence of any other string, using array scanning and hash checks …

Longest Word in Dictionary through Deleting

Find the longest word in the dictionary that can be formed by deleting characters from a string, using two-pointer scann…

K-diff Pairs in an Array

Solve K-diff Pairs in an Array by counting unique differences with a hash map or sorted two-pointer sweep.

Reverse String II

Reverse String II requires reversing segments of a string using two-pointer scanning while tracking invariants carefully…

Next Greater Element III

Find the next greater integer using the same digits as a given number with precise two-pointer scanning and invariant tr…

Reverse Words in a String III

Reverse Words in a String III involves reversing each word in a sentence using the two-pointer technique.

Permutation in String

Check if a string contains a permutation of another string using two-pointer scanning and hash table techniques.

Shortest Unsorted Continuous Subarray

Find the shortest unsorted continuous subarray that, if sorted, would sort the entire array.

Valid Triangle Number

Count all triplets in an integer array that satisfy the triangle inequality to form valid triangles efficiently using so…

Sum of Square Numbers

Given a non-negative integer c, determine if there are two integers whose squares sum to c.

Palindromic Substrings

Count all palindromic substrings in a given string using state transition dynamic programming for efficient evaluation.

Two Sum IV - Input is a BST

Determine if a binary search tree contains two nodes whose values sum to a target using efficient traversal and state tr…

Find K Closest Elements

Identify the k integers closest to a target x in a sorted array using binary search and two-pointer strategies efficient…

Valid Palindrome II

Check if a string can become a palindrome by deleting at most one character using two-pointer scanning and invariant tra…

Count Binary Substrings

Count Binary Substrings solves for the number of valid substrings with equal 0's and 1's, grouped consecutively in a bin…

Find K-th Smallest Pair Distance

Solve Find K-th Smallest Pair Distance by sorting nums, then binary searching the distance and counting valid pairs with…

Partition Labels

Partition a string into maximal parts so that each letter appears in only one segment, using two-pointer scanning.

Swap Adjacent in LR String

Transform one string into another by swapping adjacent 'L' and 'R' characters in a sequence of moves.

K-th Smallest Prime Fraction

Find the k-th smallest fraction from a sorted array of unique primes using a binary search over the answer space.

Number of Subarrays with Bounded Maximum

Count the number of contiguous subarrays with a bounded maximum value using a two-pointer approach.

Expressive Words

Expressive Words challenges you to determine if a word can be transformed into a given string by extending groups of rep…

Shortest Distance to a Character

Compute the minimum distance from each character in a string to a target character using efficient scanning techniques.

Friends Of Appropriate Ages

The Friends Of Appropriate Ages problem involves counting valid friend requests between people based on their ages with …

Most Profit Assigning Work

Assign workers to jobs maximizing total profit using difficulty, profit, and worker arrays efficiently with binary searc…

Flipping an Image

Flip each row of a binary matrix horizontally and invert its values efficiently using a two-pointer scanning approach.

Push Dominoes

In the "Push Dominoes" problem, you simulate the falling dominoes based on their initial states and determine their fina…

Backspace String Compare

Compare two strings after processing backspaces using efficient two-pointer scanning and careful invariant tracking to e…

Longest Mountain in Array

Find the length of the longest subarray forming a mountain pattern using state transitions and two-pointer logic efficie…

Advantage Shuffle

Maximize the advantage of nums1 over nums2 using a two-pointer greedy strategy, carefully tracking which elements beat o…

Middle of the Linked List

Find the middle node of a singly linked list using a two-pointer technique.

Boats to Save People

Find the minimum number of boats required to save all people, using a two-pointer approach for efficient pairing.

Sort Array By Parity

Reorder an integer array so all even numbers come before odd numbers using a precise two-pointer scanning method.

Reverse Only Letters

Reverse the characters of a string while skipping non-letter characters using a two-pointer technique.

Sort Array By Parity II

Sort an array where even numbers appear at even indices and odd numbers appear at odd indices using two-pointer scanning…

3Sum With Multiplicity

Count all unique triplets in an integer array whose sum equals the target, handling multiplicity efficiently using hashi…

Long Pressed Name

Check if a typed string could result from long pressing characters while typing a given name using a two-pointer scan.

DI String Match

Reconstruct a permutation from a DI string using two-pointer scanning, carefully tracking the increasing and decreasing …

Bag of Tokens

Maximize your score in the Bag of Tokens problem by strategically playing tokens with two-pointer scanning and greedy te…

Maximum Width Ramp

Find the maximum width of a ramp where nums[i] <= nums[j] for i < j using a two-pointer approach.

Pancake Sorting

Sort an array using pancake flips, leveraging two-pointer scanning and invariant tracking to iteratively position the la…

Squares of a Sorted Array

The problem involves squaring elements of a sorted array and returning the squares in non-decreasing order.

Interval List Intersections

This problem requires finding the intersection of two lists of intervals using a two-pointer technique with invariant tr…

Camelcase Matching

Camelcase Matching is a medium difficulty problem where you match queries to a given pattern by inserting lowercase lett…

Longest String Chain

Find the longest word chain by scanning arrays and using hash lookups to efficiently track predecessor-successor sequenc…

Duplicate Zeros

Duplicate each zero in a fixed-length array in place, shifting elements right using a two-pointer scanning approach effi…

Longest Chunked Palindrome Decomposition

Solve the "Longest Chunked Palindrome Decomposition" problem by using dynamic programming and string manipulation techni…

Last Substring in Lexicographical Order

Identify the lexicographically last substring in a string using two-pointer scanning with invariant tracking efficiently…

Find Positive Integer Solution for a Given Equation

Determine all positive integer pairs that satisfy a hidden monotonic function for a given target using binary search ove…

Remove Palindromic Subsequences

This problem challenges you to remove palindromic subsequences from a string with a minimum number of steps using two-po…

Check If N and Its Double Exist

Solve Check If N and Its Double Exist by scanning once and checking doubles or halves in a hash set.

Find the Distance Value Between Two Arrays

Calculate the distance value between two integer arrays by determining how many elements in arr1 don't have a close coun…

Check If a Word Occurs As a Prefix of Any Word in a Sentence

Determine the first word in a sentence where a given searchWord is a prefix using two-pointer scanning with string match…

The k Strongest Values in an Array

Identify the k strongest values in an array using two-pointer scanning and careful tracking of the array's centre value.

Number of Subsequences That Satisfy the Given Sum Condition

Count all non-empty subsequences in an integer array where the sum of the minimum and maximum elements is at most a targ…

Range Sum of Sorted Subarray Sums

Compute the sum of sorted subarray sums efficiently using binary search over valid sum ranges and prefix sum accumulatio…

Get the Maximum Score

Find the maximum possible score from two sorted arrays with a dynamic programming approach, leveraging partitioning and …

Shortest Subarray to be Removed to Make Array Sorted

Find the shortest subarray to remove in order to make an array non-decreasing using binary search and two-pointer techni…

Number of Ways Where Square of Number Is Equal to Product of Two Numbers

Find the number of triplets where the square of a number equals the product of two others, utilizing array scanning and …

Split Two Strings to Make Palindrome

Determine if splitting two equal-length strings at a common index can form a palindrome using two-pointer scanning techn…

Max Number of K-Sum Pairs

Max Number of K-Sum Pairs is a problem involving counting disjoint pairs with a given sum k in an array.

Checking Existence of Edge Length Limited Paths

Solve the problem of checking if there exists a path between two nodes under edge length constraints using efficient tec…

Ways to Split Array Into Three Subarrays

The problem requires finding the number of ways to split an array into three subarrays where each split meets a certain …

Swapping Nodes in a Linked List

Swap nodes in a linked list using linked-list pointer manipulation and two pointers to solve this medium difficulty prob…

Minimum Length of String After Deleting Similar Ends

Minimize string length by deleting similar characters from both ends repeatedly using a two-pointer technique.

Largest Merge Of Two Strings

Construct the lexicographically largest merge from two strings using a two-pointer greedy scanning approach efficiently.

Closest Subsequence Sum

Find the minimum absolute difference between a target goal and any subsequence sum using optimized dynamic programming a…

Form Array by Concatenating Subarrays of Another Array

Determine if you can sequentially select disjoint subarrays from nums matching each group in order using two-pointer sca…

Merge Strings Alternately

Merge two strings alternately, starting with the first string, and append extra characters when one string is longer.

Count Pairs Of Nodes

Given a graph with nodes and edges, count pairs of nodes where the degree sum exceeds a given threshold for each query.

Maximum Score of a Good Subarray

Maximize the score of a good subarray using binary search to explore the valid answer space with a focus on two-pointer …

Sentence Similarity III

Sentence Similarity III asks if one sentence can be transformed into another by inserting a sentence inside it.

Minimum Adjacent Swaps to Reach the Kth Smallest Number

Find the minimum number of adjacent swaps to reach the kth smallest wonderful integer from a given number string.

Maximum Distance Between a Pair of Values

Find the maximum distance between a pair of values in two non-increasing integer arrays using binary search.

Rotating the Box

Rotate a box represented by a character matrix, letting stones fall under gravity using precise two-pointer scanning and…

Minimize Maximum Pair Sum in Array

Minimize the maximum pair sum in an array by optimally pairing its elements.

Maximum Number of Removable Characters

Use binary search and a subsequence check to find the largest removable prefix that still keeps p inside s.

Check If String Is a Prefix of Array

Determine if a string is a prefix of an array by concatenating initial elements, using two-pointer scanning efficiently.

Minimum Number of Swaps to Make the String Balanced

Determine the minimum swaps to balance a bracket string using two-pointer scanning with invariant tracking efficiently.

Reverse Prefix of Word

Reverse the prefix of a string starting from index 0 to the first occurrence of a given character.

Partition Array Into Two Arrays to Minimize Sum Difference

Partition an integer array into two equal halves to minimize the absolute difference of their sums using dynamic program…

Maximum Number of Tasks You Can Assign

Maximize the number of tasks that can be completed by efficiently using workers and magical pills.

Delete the Middle Node of a Linked List

Efficiently remove the middle node from a linked list using two-pointer techniques and careful pointer updates to mainta…

Watering Plants II

Simulate watering a row of plants with Alice and Bob using two-pointer scanning, tracking refills precisely for each ste…

Find First Palindromic String in the Array

Return the first palindromic string from an array of words or an empty string if none exists.

Adding Spaces to a String

Learn to efficiently insert spaces in a string using two-pointer scanning with invariant tracking in linear time.

Recover the Original Array

Recover the Original Array helps you understand how to reverse-engineer an array from two subsets using array scanning a…

Maximum Twin Sum of a Linked List

Find the maximum twin sum in a linked list by manipulating pointers efficiently and leveraging stack or reversal techniq…

Rearrange Array Elements by Sign

Rearrange an array by alternating positive and negative integers using a two-pointer approach with invariant tracking.

Partition Array According to Given Pivot

Rearrange an array around a pivot while maintaining relative order using a two-pointer scanning approach efficiently.

Minimum Number of Moves to Make Palindrome

The problem challenges you to find the minimum number of adjacent swaps to make a string a palindrome.

Find All K-Distant Indices in an Array

Identify all indices in an array that are within k distance of elements equal to the given key using two-pointer scannin…

Maximum Total Beauty of the Gardens

Determine the maximum total beauty of gardens by strategically planting flowers using binary search over achievable flow…

Successful Pairs of Spells and Potions

Count how many potions pair successfully with each spell using binary search over sorted potion strengths efficiently.

The Latest Time to Catch a Bus

Find the latest time to catch a bus based on departure times, passenger arrivals, and capacity using binary search over …

Move Pieces to Obtain a String

Determine if the pieces in start can be moved to form target using two-pointer scanning and strict left-right movement r…

Number of Arithmetic Triplets

Count the number of arithmetic triplets in a given strictly increasing array with a specified difference.

Strictly Palindromic Number

Determine if a number is strictly palindromic in all bases from 2 to n minus 2 using two-pointer scanning and invariant …

Divide Intervals Into Minimum Number of Groups

Determine the minimum number of non-overlapping groups for a set of intervals using precise two-pointer scanning logic.

Maximum Matching of Players With Trainers

Maximize the number of valid player-trainer matchings using two-pointer scanning and careful sorting strategy.

Largest Positive Integer That Exists With Its Negative

Find the largest positive integer in an array such that its negative counterpart also exists.

Apply Operations to an Array

Transform an array by applying adjacent doubling operations and shifting zeros efficiently using two-pointer scanning te…

Total Cost to Hire K Workers

Optimize the total cost of hiring exactly k workers using a two-pointer approach with invariant tracking and priority qu…

Number of Distinct Averages

Calculate the number of unique averages formed by repeatedly pairing smallest and largest elements efficiently using has…

Maximum Number of Non-overlapping Palindrome Substrings

Find the maximum number of non-overlapping palindromic substrings of at least length k in a string using dynamic program…

Append Characters to String to Make Subsequence

Determine the minimum characters to append to s so t becomes a subsequence using efficient two-pointer scanning techniqu…

Divide Players Into Teams of Equal Skill

Divide players into equal skill teams and return the sum of their chemistry, or -1 if impossible.

Maximum Number of Points From Grid Queries

Solve the Maximum Number of Points From Grid Queries problem using two-pointer scanning and invariant tracking.

Maximum Enemy Forts That Can Be Captured

Find the maximum number of enemy forts that can be captured by moving your army using two-pointer scanning with invarian…

Minimum Common Value

Find the smallest integer appearing in both sorted arrays efficiently using array scanning and hash-based lookup techniq…

Find the Array Concatenation Value

Compute the array concatenation value efficiently using two-pointer scanning while maintaining a running total of concat…

Count the Number of Fair Pairs

Efficiently count all fair pairs in an array using sorting and binary search, focusing on the sum range between lower an…

Subsequence With the Minimum Score

Find the minimum score of a string by removing characters from t while maintaining subsequence validity with s.

Merge Two 2D Arrays by Summing Values

Merge two 2D arrays by summing values with matching ids using array scanning and hash lookup efficiently.

Find the Maximum Number of Marked Indices

Maximize marked indices in an array by performing allowed operations, applying binary search to find the optimal count e…

Maximize Greatness of an Array

Maximize Greatness of an Array requires permuting numbers to exceed original values at most indices efficiently.

Lexicographically Smallest Palindrome

Given a string, make it a palindrome with the fewest operations, prioritizing lexicographically smallest result.

Count Pairs Whose Sum is Less than Target

This problem asks you to count all index pairs in an array whose sum is strictly less than a given target value efficien…

Make String a Subsequence Using Cyclic Increments

Determine if str2 can be made a subsequence of str1 by incrementing characters cyclically using at most one operation.

Minimum Array Length After Pair Removals

This problem involves minimizing the length of a sorted array by repeatedly removing adjacent pairs of equal elements.

Find Indices With Index and Value Difference I

Find two indices in an array where their difference in both index and value meets specified thresholds.

Find Indices With Index and Value Difference II

Locate two indices in an array where both index and value differences meet specified thresholds using precise scanning t…

Minimum Changes to Make K Semi-palindromes

Minimize the number of letter changes to partition a string into k semi-palindromes using dynamic programming and two po…

Separate Black and White Balls

Solve the "Separate Black and White Balls" problem by swapping adjacent balls to group all black balls to the right with…

Count the Number of Incremovable Subarrays I

Count the number of incremovable subarrays in an array by removing them to create a strictly increasing sequence.

Count the Number of Incremovable Subarrays II

Count the number of incremovable subarrays where removal of the subarray results in a strictly increasing array.

Find Beautiful Indices in the Given Array I

Identify all beautiful indices where substring a appears and a nearby substring b exists within distance k efficiently.

Find Beautiful Indices in the Given Array II

Find Beautiful Indices in the Given Array II challenges you to use binary search and string matching techniques.

Find the Integer Added to Array II

Given two arrays nums1 and nums2, determine the integer added to nums1 to make it equal to nums2 after removing two elem…

Maximum Total Damage With Spell Casting

Calculate the maximum total damage by selectively casting spells while avoiding adjacent power conflicts using array sca…

Minimum Average of Smallest and Largest Elements

Solve the Minimum Average of Smallest and Largest Elements problem using two-pointer scanning to track averages effectiv…

Minimum Number of Flips to Make Binary Grid Palindromic I

Find the minimum flips to make a binary grid palindromic by scanning with two pointers and tracking symmetry efficiently…

Minimum Number of Flips to Make Binary Grid Palindromic II

The problem asks to flip cells in a binary grid to make its rows and columns palindromic using the minimum number of fli…

Find the Lexicographically Smallest Valid Sequence

Determine the lexicographically smallest valid index sequence by using state transition dynamic programming over word1 a…

Find Maximum Removals From Source String

Determine the maximum number of characters you can remove from source while keeping pattern as a subsequence using array…

Find the Lexicographically Largest String From the Box I

This problem involves finding the lexicographically largest string from a given word using a two-pointer approach.

Shortest Matching Substring

Find the shortest substring in a string that matches a pattern with exactly two wildcards efficiently using binary searc…

Longest Palindrome After Substring Concatenation I

Compute the maximum palindrome length by concatenating substrings from two strings using state transition dynamic progra…

Longest Palindrome After Substring Concatenation II

Compute the longest palindrome by concatenating substrings from two strings using state transition dynamic programming e…

Maximum Product of First and Last Elements of a Subsequence

Maximize the product of the first and last elements of any subsequence of size m in an integer array.