剑指 Offer 48. 最长不含重复字符的子字符串

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        unordered_map<char, int> pre;
        int left, right;
        left = right = 0;
        int maxlen = 0;
        for(int i=0;i<s.size();++i){
            char ch = s[right];
            auto preIt = pre.find(ch);
            //如果没找到或者在left之前
            if(preIt == pre.end() || preIt->second < left){
                pre[ch] = right;
                right++;
                if(right == s.size()){
                    int nowlen = right - left;
                    maxlen = max(maxlen, nowlen);
                }
            }else{
                //left到right之间有重复
                int nowlen = right - left;
                maxlen = max(maxlen, nowlen);
                left = pre[ch]+1;
                pre[ch] = right;
                right++;
            }
        }
        return maxlen;
    }
};**