[LeetCode] #3 Longest Substring Without Repeating Characters

今天清明，再补一篇

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.

input：abcabcbb

output：abc

这篇其实我先将字符中的各种字符存在str_map中，然后通过设定初始位子以及各字符的最后出现的位置来判定子串的开始位置和子串的长度。时间复杂度O(n)，时间：122ms

代码如下：

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        map<char, int> str_map;
        int maxlen = 0, flag = -1;
        for (int i = 0; i < s.size(); i++){
            if (!str_map.count(s[i])){
                str_map.insert(make_pair(s[i], -1));
            }
        }
        for (int i = 0; i < s.size(); i++){
            if (str_map[s[i]]>flag)
                flag=str_map[s[i]];
            if (i - flag > maxlen)
                maxlen = i - flag;
            str_map[s[i]] = i;
        }
        return maxlen;
    }
};