Longest Substring Without Repeating Characters

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题目：

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.

分析：遍历字符串，设置一个起始点，一个终点，若碰到重复字符，则改变起始点。算法最坏情况下的时间复杂度为O（n^2），当然，若利用hash查找时间复杂度可降至O（n）

代码如下：

int search(string s,int start,int end)
    {
        for(int i=end-1;i>=start;i--)
        {
            if(s[i]==s[end])return (i+1);
        }
        return start;
    }
    int lengthOfLongestSubstring(string s)
    {
        int n=s.length();
        if(n<=1)return n;
        int start=0,max=1;
        for(int i=1;i<n;i++)
        {
            start=search(s,start,i);
            if((i-start+1)>max)
            {
                max=i-start+1;
            }
        }
        return max;
    }