弟中弟的Leetcode总结——字符串类（一）

弟中弟的Leetcode总结——字符串类（一）

题目描述

Longest Substring

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

Example 1:
Input: “abcabcbb”
Output: 3
Explanation: The answer is “abc”, which the length is 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.

思路

开始的想法是用动态规划以及访问表来做，类似于最大子序列之和，但是后面发现存在的问题是：如果遇到了重复的字符，不能直接将长度重置为0，应该返回到重复的字符的后一个字符，再向后扫描。

代码（C）

int lengthOfLongestSubstring(char* s) {
    int len = strlen(s);
    int visit[1000];
    int begin = 0;//begin是子字符串开始的下标
    int count = 0, temp = 0;
    memset(visit,0,sizeof(visit));
    for(int i = 0; i < len; i++){
        //如果没有遇到过重复，则一直增大temp
        if(visit[s[i]] == 0){
            temp++;
            end = i;
            visit[s[i]] = 1;
        }
        else{
            //遇到重复的时候，首先返回到前面重复的字符的后一个
            for(int k = i-1; k >= begin; k--){
                if(s[k] == s[i]){
                    begin = k + 1;
                    break;
                }
            }
            //重置访问表
            memset(visit,0,sizeof(visit));
            for(int k = begin; k <= i; k++)
                visit[s[k]] = 1;
            //更新temp
            temp = i -begin + 1;
        }
        if(temp > count)
            count = temp;
    }
    return count;
}