3.Longest Substring Without Repeating Characters

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Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

Example 2:

Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3. 
             Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

Solution:

public class Solution {
	public int lengthOfLongestSubstring(String s) {
		int n = s.length();
		int ans = 0;
		for (int i = 0; i < n; i++)
			for (int j = i + 1; j <= n; j++)
				if (allUnique(s, i, j)) ans = Math.max(ans, j - i);
		return ans;
	}

	public boolean allUnique(String s, int start, int end) {
		Set<Character> set = new HashSet<>();
		for (int i = start; i < end; i++) {
			Character ch = s.charAt(i);
			if (set.contains(ch)) return false;
			set.add(ch);
		}
		return true;
	}
}

参考原文