[leetcode]3. Longest Substring Without Repeating Characters
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题目地址
https://leetcode.com/problems/longest-substring-without-repeating-characters/
题目大意
从字符串中找出最长的不重复子串的长度
解题思路
最暴力的解法是两次循环遍历,显然这道题这么解会超时。所以需要降低时间复杂度。有没有办法一次遍历就解决呢。为此,需要引入一些辅助变量来帮助我们记录一些中间信息。首先想到的就是要记录每个字符最后出现的位置,用last
数组表示。帮助我们快速判断与当前字符重复的最近的字符位置。其次,还需要引入一个变量start
来记录当前非重复子串的起始位置。在遍历时,遇到与当前字符s[i]
重复的字符s[k]
时,更新起始位置为start = k + 1
。
代码
class Solution {public: int lengthOfLongestSubstring(string s) { int size = s.size(); int len = 0; int start = 0; int last[128]; memset(last, 0xff, sizeof(int) * 128); for (int i = 0; i != s.size(); ++i) { if (last[s[i]] >= start) { len = len > (i - start) ? len : (i - start); start = last[s[i]] + 1; } last[s[i]] = i; } return len > (size - start) ? len : (size - start); }};
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