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1
int 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;
}
}