[LeetCode] 3. Longest Substring Without Repeating Characters

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

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int[] flag = new int[256];
        for (int i = 0; i < flag.length; i++) {
            flag[i] = -1;
        }
        int maxLen = 0;
        int start = 0;
        for (int i = 0; i < s.length(); i++) {
            int pos = flag[(int)s.charAt(i)];
            if (pos >= start) {
                maxLen = Math.max(maxLen, i - start);
                start = pos + 1;
            }
            flag[(int)s.charAt(i)] = i;
        }
        return Math.max(maxLen, s.length() - start);
    }
}