LeetCode——003 Longest Substring Without Repeating Characters

Description

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.

** Solution: **

使用unordered_map来记录重复字母出现的最右端位置，然后使用现在的位置减去重复字母位置，中间就是没有重复字母的子串了

class Solution {
public:
    int lengthOfLongestSubstring(string s) {               
        int res = 0, L = -1;
        unordered_map<char, int>map;//用来记录字母出现的最右端位置
        for (int i = 0; i < s.length(); ++i)
        {
            if (map.find(s[i]) != map.end())
                L = max(L, map[s[i]]);
            map[s[i]] = i;
            res = max(res, i - L);
        }
        return res;
    }
};