leetcode--Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest substring is "b", with the length of 1.

public class Solution {    public int lengthOfLongestSubstring(String s) {        int[] flag = new int[256];//记录当前子串中出现过的字符Arrays.fill(flag, -1);//初始值为1int start = 0;//子串起始位置int max = 0;//子串最大长度int i=0;for(i=0;i<s.length();i++){if(flag[s.charAt(i)]==-1){//如果改字符没有被记录过flag[s.charAt(i)] = i;//记录字符对应位置，标记为记录过}else{//如果出现重复字符if(max<i-start) max = i-start;//修改最大值i = flag[s.charAt(i)];//由子串中重复字符出现的位置重新计算start = i+1;//更新起始位置Arrays.fill(flag, -1);//复位}}if(max<i-start) max = i-start;//到了末尾，还要算一次return max;    }}