LeetCode-3_Longest_Substring_Without_Repeating_Characters

#include <iostream>
#include<ext/hash_map>

/*
2017年10月14日15:23:32

Given a string, find the length of the longest substring without repeating characters.
Examples:
Given "abcabcbb", the answer is "abc", which the length is 3.  Given "bbbbb", the answer is "b", with the length of 1.
Given "pwwkew", the answer is "wke", with the length of 3.
Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
*/

using namespace std;
using namespace __gnu_cxx;      //hash_map的命名空间

class Solution {
public:
    static int lengthOfLongestSubstring(string s) {
        int ret = 0,times = 0;
        hash_map<char,int> exists;
        for(auto c : s){
            if(exists.find(c) == exists.end()){
                ++times;
                exists[c] = 1;
                ret = (times > ret) ? times : ret;      //如果没有这句话，当传入string的整体满足不重复substring的条件时，将导致结果为0;例：传入"abcde"结果为0而不是5
            }
            else{
                if(times > ret){
                    ret = times;
                }
                times = 1;              //将这个字母作为下一个sunstring的首字母，因此初值为1
                exists.clear();
                exists[c] = 1;          //做上标记：该字母已出现1次
            }
        }

        return ret;
    }
};

int main()
{
    string s = string("pwwkew");
    auto ret = Solution::lengthOfLongestSubstring(s);
    cout << ret << endl;

    return 0;
}