Leetcode 3. Longest Substring Without Repeating Characters

3. Longest Substring Without Repeating Characters

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.

题目链接：https://leetcode.com/problems/longest-substring-without-repeating-characters/description/

题目大意：找到给定字符串中的最大字串，要求字串中字母不重复。

解题思路：纪录初始起点下标 st  ＝ 0，遍历字符串，用 map 标记从起始位置 st 到当前位置的字串中每个字母的出现次数，如果访问到重复字母，则纪录字串最大长度并更新起始位置 st 及更新map 标记的值。

代码：

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int len = s.length();
        if (len == 0)
            return 0;
        else if(len == 1)
            return 1;
        int ans = 1,st = 0;
        map  mp;
        mp[s[0]] = 1;
        for(int i = 1;i < len;i ++){
            if(mp[s[i]]){
                ans = max(ans,i - st);
                while(mp[s[i]] && st < i){
                    mp[s[st]] -- ;
                    st ++ ;
                }
                mp[s[i]] ++ ;
            }else{
                mp[s[i]] ++;
            }
        }
        ans = max(ans,len - st);
        return ans;
    }
};