hash table plus string Pattern
58 problems
Pattern pages help build reusable solving frames. Identify signals first, then explain state, transition, and edge handling.
Recognition Signals
- Check if the candidate correctly identifies the need for two hash maps to track character mappings.
- Evaluate the candidate's ability to ensure bijective character mappings without conflicts.
- They may ask about handling large alphabets efficiently with hash maps.
Solve Flow
- 1. Define the active state/window.
- 2. Update state while preserving invariants.
- 3. Validate with edge-heavy examples.
Common Misses
- Not checking for bijective mapping, which can cause mapping conflicts where multiple characters map to the same character.
- Forgetting to mark the end-of-word flag, causing search to fail on full words.
- Using a hash table can lead to excessive space usage for large inputs.
Recommended Ladder
Isomorphic Strings
Determine if two strings are isomorphic by checking if one string can be transformed into the other using character repl…
Implement Trie (Prefix Tree)
This problem requires designing a Trie (Prefix Tree) to efficiently store and query strings using hash table concepts fo…
Valid Anagram
Check if two strings are anagrams using hashing or sorting techniques.
Word Pattern
Solve Word Pattern by checking a one-to-one mapping between pattern letters and words using hash tables after splitting …
Bulls and Cows
Solve the Bulls and Cows problem using hash tables and string manipulation to track exact and misplaced digits.
Ransom Note
Determine if a ransom note can be constructed from a magazine's letters using hash tables and string counting techniques…
Find the Difference
Find the Difference involves identifying the additional letter in one string compared to another, emphasizing hash table…
Encode and Decode TinyURL
Design a class that encodes and decodes URLs using a URL shortening approach based on hash tables and strings.
Map Sum Pairs
Design and implement a data structure that supports efficient insertion and sum queries based on string prefixes.
Jewels and Stones
Given two strings, determine how many of the stones you have are also jewels, considering case sensitivity.
Custom Sort String
Sort the string `s` according to a custom order defined by string `order`.
Buddy Strings
Determine if two strings can become equal by swapping exactly two letters using a hash table for character tracking.
Uncommon Words from Two Sentences
Find uncommon words from two sentences by counting word frequencies using hash tables.
Alphabet Board Path
Find the path to type a target string on an alphabet board using directional moves and the 'hash table plus string' patt…
Maximum Number of Balloons
Find the maximum number of times the word 'balloon' can be formed from characters of the given string.
Minimum Number of Steps to Make Two Strings Anagram
Calculate the minimum steps to transform one string into an anagram of another using character replacements efficiently.
Increasing Decreasing String
Reorder the string based on a specific algorithm using hash tables and string manipulation.
Design Underground System
Design an underground system to calculate travel times between stations using hash tables for efficient lookups and aver…
HTML Entity Parser
Transform a string containing HTML entities into their character equivalents using a hash table for efficient parsing.
Check If a String Contains All Binary Codes of Size K
Determine if every possible binary string of length k exists as a substring within a given binary string s efficiently u…
Path Crossing
Check if a path crosses itself on a 2D plane using a hash table to track visited points during traversal.
Can Convert String in K Moves
Determine if string s can be transformed into t within k moves using character shifts and hash table counting efficientl…
Find Longest Awesome Substring
Find the maximum-length awesome substring in a numeric string using hash table and bit manipulation for palindrome poten…
Largest Substring Between Two Equal Characters
Find the longest substring between two equal characters using a hash table for optimized performance.
Determine if Two Strings Are Close
Check if two strings can transform into each other using letter swaps and frequency reorganizations, leveraging hash tab…
Sum of Beauty of All Substrings
Calculate the total beauty of all substrings by counting character frequencies and computing frequency differences effic…
Check if One String Swap Can Make Strings Equal
Check if one string swap can make two equal strings using hash table and string counting methods.
Second Largest Digit in a String
Given a string with alphanumeric characters, find the second largest digit, or return -1 if it doesn’t exist.
Number of Different Integers in a String
Count all unique integers in a string by replacing letters and handling leading zeros correctly with a hash table approa…
Check if the Sentence Is Pangram
Determine if a given lowercase string contains every English letter using efficient hash table tracking techniques.
Redistribute Characters to Make All Strings Equal
Determine if you can redistribute characters among strings so that all strings become identical using a counting approac…
Maximum Number of Words You Can Type
Determine how many words can be typed on a malfunctioning keyboard with some broken keys.
Check if All Characters Have Equal Number of Occurrences
Check if a string has characters with equal occurrences using hash tables and string manipulation techniques.
Count Vowel Substrings of a String
Count the number of vowel substrings that include all five vowels in a string.
Check Whether Two Strings are Almost Equivalent
Solve Check Whether Two Strings are Almost Equivalent by counting letters and rejecting any character whose frequency ga…
Rings and Rods
Count how many rods have all three colors using a hash table to track colors per rod efficiently in strings.
Minimum Number of Steps to Make Two Strings Anagram II
Compute the fewest character insertions needed to turn two strings into anagrams using hash table frequency counts effic…
Check if Number Has Equal Digit Count and Digit Value
Determine if a number's digits correspond to their counts in the string representation.
Rearrange Characters to Make Target String
Calculate the maximum copies of a target string from letters in s using frequency counting and hash tables efficiently.
Greatest English Letter in Upper and Lower Case
Find the greatest English letter that exists in both lowercase and uppercase in a string using a hash table approach.
Decode the Message
Decode the Message is an easy problem involving hash table mapping for string decoding based on a cipher key.
First Letter to Appear Twice
Find the first letter that repeats in a string using hash table tracking and early detection for efficiency.
Remove Letter To Equalize Frequency
Determine if removing a single letter from a string can make all remaining letters have identical frequency efficiently.
Make Number of Distinct Characters Equal
Determine if a single swap can equalize distinct character counts between two strings using hash tables for tracking fre…
Minimize String Length
Minimize String Length asks you to reduce a string by removing duplicates using a Hash Table strategy efficiently.
Check if Strings Can be Made Equal With Operations II
Check if two strings can be made equal using operations that swap characters with the same parity.
Existence of a Substring in a String and Its Reverse
Check for any substring of length 2 in a string and its reverse using a hash table and string comparison.
Count the Number of Special Characters I
Count the number of special characters in a given string using hash tables and string manipulation.
Count the Number of Special Characters II
Count the Number of Special Characters II is a medium difficulty string and hash table problem that involves identifying…
Minimum Number of Operations to Make Word K-Periodic
The problem requires calculating the minimum number of operations to make a string k-periodic using specific substring r…
Minimum Length of Anagram Concatenation
The problem asks to find the minimum length of a string t such that s is a concatenation of anagrams of t.
Permutation Difference between Two Strings
Compute the total index difference between two strings by mapping characters and summing their positional distances effi…
Minimum Length of String After Operations
Find the minimum length of a string after performing operations based on character frequency.
Rearrange K Substrings to Form Target String
Determine if s can be split into k equal substrings and rearranged to match t using a hash table for frequency tracking.
Find Valid Pair of Adjacent Digits in String
Identify the first valid adjacent digit pair in a string where each digit appears exactly as many times as its numeric v…
Maximum Difference Between Even and Odd Frequency I
Find the maximum difference between the frequency of characters in a string with odd and even frequencies.
Find Most Frequent Vowel and Consonant
Given a string, calculate the sum of the most frequent vowel and consonant frequencies.
Partition String
Partition a string into unique segments using hash table and string manipulation.