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.

<span style="color:#333333;">class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int a[256];
        memset(a,0,256*4);
        int i=0;
        int sum=0;
        int max=0;
        while(i<s.length()){
            if(a[(int)s[i]]==0){
                </span><span style="color:#ff0000;">a[(int)s[i]]</span><span style="color:#333333;">=i+1;//存储保证字符出现的下标,从1开始,是为了避免和a[(int)s[i]]==0冲突
                sum++;
                if(sum>max){
                    max=sum;
                }
                i++;
            }else{
                </span><span style="color:#ff6666;">i=a[(int)s[i]];</span><span style="color:#333333;">
                memset(a,0,256*4);
                sum=0;
            }
        }
        if(sum>max){
            max=sum;
        }
        return max;
    }
};</span>