LeetCode 3. Longest Substring Without Repeating Characters（最长不重复子串）

原题网址：https://leetcode.com/problems/longest-substring-without-repeating-characters/

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

Examples:

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", 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.

方法：通过哈希表/直方图来标记字符是否出现过。

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        if (s == null) return 0;
        boolean[] has = new boolean[256];
        int max = 0;
        int from = 0;
        char[] sa = s.toCharArray();
        for(int i=0; i<sa.length; i++) {
            while (has[sa[i]]) has[sa[from++]] = false;
            has[sa[i]] = true;
            max = Math.max(max, i-from+1);
        }
        return max;
    }
}