#2414

Medium

auto_awesomeString-driven solution strategy

LeetCode Problem Workspace

Length of the Longest Alphabetical Continuous Substring

Find the length of the longest continuous alphabetical substring from a given string of lowercase letters.

Problem Statement

You are given a string s consisting of lowercase letters. Your task is to find the length of the longest substring in which the characters appear in alphabetical order. A substring is considered in alphabetical order if each character is followed by the next character in the alphabet.

For example, the substring "abc" is in alphabetical order, but "acb" is not. The input string can vary in length, with up to 100,000 characters. You need to implement an efficient solution that handles the maximum input size within time and space limits.

Examples

Example 1

Input: s = "abacaba"

Output: 2

There are 4 distinct continuous substrings: "a", "b", "c" and "ab". "ab" is the longest continuous substring.

Example 2

Input: s = "abcde"

Output: 5

"abcde" is the longest continuous substring.

Constraints

1 <= s.length <= 105
s consists of only English lowercase letters.

Solution Approach

Iterate Through the String

To identify the longest alphabetical continuous substring, iterate through the string comparing adjacent characters. Keep track of the length of the current continuous substring, and update the maximum length when a new substring starts.

Track Length of Substrings

Maintain two variables: one for the current length of the alphabetical substring and another for the longest length encountered. Reset the current length when the sequence breaks and update the longest length when needed.

Handle Edge Cases

Ensure that single-character substrings or strings with no continuous alphabetical order are handled correctly. A string of length one will have a continuous substring of length one, and the algorithm should be able to handle strings where no characters form an alphabetical sequence.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

The time complexity of the solution is O(n), where n is the length of the input string. This is because we are iterating through the string once. The space complexity is O(1) since we only need a few variables to keep track of the current and longest lengths.

What Interviewers Usually Probe

Ability to track the longest substring efficiently
Effective use of variables to maintain substring length
Clear understanding of edge cases and constraints

Common Pitfalls or Variants

Common pitfalls

Overcomplicating the problem with unnecessary nested loops
Not properly handling edge cases such as strings of length one or no alphabetical sequences
Failure to update the longest substring correctly during iteration

Follow-up variants

Consider different ways to scan through the string, such as using sliding window techniques
Extend the problem to handle uppercase letters as well
Modify the problem to return the actual substring instead of just its length

FAQ

What is the main approach for solving the Length of the Longest Alphabetical Continuous Substring problem?

The key approach is to iterate through the string, comparing adjacent characters, and keep track of the longest continuous substring that appears in alphabetical order.

How do I handle cases where the string is too short for a meaningful alphabetical substring?

In such cases, a single-character string would have the longest alphabetical substring of length 1. Ensure that this edge case is handled.

What happens when no characters form an alphabetical sequence?

If no characters form a continuous alphabetical sequence, each individual character is considered its own substring, and the length of the longest substring will be 1.

How does the problem relate to the string-driven solution strategy?

This problem is a prime example of using a string-driven approach where you manipulate and process a string character by character to identify patterns or substrings.

What is the time complexity of the solution for the Length of the Longest Alphabetical Continuous Substring problem?

The time complexity of the optimal solution is O(n), where n is the length of the string, as we process each character once.

terminal

Solution

Solution 1: Single Pass

We can traverse the string $s$ and use a variable $\textit{ans}$ to record the length of the longest lexicographically consecutive substring, and another variable $\textit{cnt}$ to record the length of the current consecutive substring. Initially, $\textit{ans} = \textit{cnt} = 1$.

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class Solution:
    def longestContinuousSubstring(self, s: str) -> int:
        ans = cnt = 1
        for x, y in pairwise(map(ord, s)):
            if y - x == 1:
                cnt += 1
                ans = max(ans, cnt)
            else:
                cnt = 1
        return ans

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