算法练习笔记（十六）—— 最长的子串

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本文探讨了LeetCode上一道经典题目：寻找给定字符串中最长的无重复字符子串。通过实例说明了如何判断子串是否包含重复字符，并提供了一种遍历字符串的方法来求解该问题。

在leetcode上面练习题目的时候，经常会有子串（subsequence）和子集（substring）的区别，区分就在于子串总是连续的，而子集可以是字符串内任意字符的组合

题目：Longest Substring Without Repeating Characters

地址：https://leetcode.com/problems/longest-substring-without-repeating-characters/#/description

描述：

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.

解析：

由于对于时间复杂度没有太高的要求，因此我们可以直接遍历

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int len = s.size();
        if(len < 2)return len;
        int key = 1;
        for(int i = 0; i < len - 1; i ++){
            if(s[i] != s[i + 1]){
                int count = 2;      
                for(int j = i + 2; j < len; j ++){
                    int flag = 0;
                    for(int k = 1; k <= count; k ++){
                        if(s[j - k] == s[j])break;
                        if(k == count)flag = 1;
                    }
                    if(flag == 0)break;
                    count++;
                }
                key = max(key, count);
            }
        }
        return key;
    }
};