LC 3. Longest Substring Without Repeating Characters

题目描述

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.

参考答案

 class Solution {
 public:
     int lengthOfLongestSubstring(string s) {

         unordered_map<char,int> map;
         int res = ;
         int start = -; // 存储开始的位置，如果完全没有重复的字符，那么开始位置永远是-1

         for(int i = ;i<s.length();i++){
             if(map.find(s[i]) != map.end()){
                 start = max(start,map[s[i]]);
                 // 如果通过find 找到了一个重复的
                 // 那么就把start给替换成 上一个重复字符的index
             }
             map[s[i]] = i; // map[char] = index;
             res = max(res,i-start); // 获得最大值
         }
         return res;
     }
 };    

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.