Longest Substring Without Repeating Characters
Given a string, find the longest substring that does not contain any repeated characters.
Example 1:
Input: "abcabcbb"
Output: "abc"
Explanation: The longest substring without repeating characters is "abc".Example 2:
Input: "bbbbb"
Output: "b"
Explanation: The longest substring without repeating characters is "b".Example 3:
Input: "pwwkew"
Output: "wke"
Explanation: The longest substring without repeating characters is "wke".Implement the following method:
class Solution {public String longestSubstring(String s) {}}This problem asks for the longest substring without repeating characters. The standard solution uses a sliding window with a hash set or hash map to track characters in the current window. Expand the right pointer as long as characters remain unique, and move the left pointer forward when a duplicate appears. This gives an efficient linear-time approach and matches the sample cases such as fully unique, fully repeated, and mixed-character strings.
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