LeetCode刷题笔记（Longest Substring Without Repeating Characters）

大家新年好，今天刷了新年后的第一道题，整体感觉还行，下面来分享下做题的经验吧！

具体题目如下：

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.

题意分析： 

给定一个字符串，找到没有重复字符的最长连续子串，且返回该子串的长度。

解答如下：

方法一（滑动窗格法）

用两个指针l、r同时指向数组左端，l指针先增加与r指针构成一个滑动窗格，另外r指针每往前指向一个元素，需要用freq数组去记录其出现的次数，并用于判断滑动窗格中是否有重复的元素。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int freq[256] = {0};  //用于记录字符出现的次数
        int l = 0, r = -1;    
        int res = 0;

        while( l < s.size() ){
            if (r+1 < s.size() && freq[s[r+1]] == 0)
                freq[s[++r]] ++;
            else
                freq[s[l++]] --;

            res = max( res, r-l+1 );
        }
        return res;
    }
};

提交后的结果如下：

 

日积月累，与君共进，增增小结，未完待续。   

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