leetcode 3. Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3
Explanation: 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.

 

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int i = 0, j = 0;
        map<char, int> mp; //值映射的是字符所在的下标位置
        int len = s.length(); //字符串的长度
        vector<int> dp(len, 0); //dp[j]表示以第j个字符结尾的不重复子串的长度
        int maxn = 0;
        for (j = 0; j < len; j++) {
            //如果当前的字符已经之前出现过了，并且是在i之后位置的，那么要更新窗口左边的下标
            if (mp.count(s[j]) > 0) { 
                i = max(i, mp[s[j]] + 1);
            }
            dp[j] = j - i + 1; //窗口大小即为以第j个字符结尾的最长不重复子串的长度
            mp[s[j]] = j;
            maxn = max(maxn, dp[j]);
        }
        return maxn;
    }
};