53 lines
1.5 KiB
Markdown
53 lines
1.5 KiB
Markdown
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## 题目地址
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https://leetcode-cn.com/problems/implement-strstr/
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## 思路
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KMP 经典算法
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KMP的经典思想是:当出现字符串不匹配时，可以记录一部分之前已经匹配的文本内容，利用这些信息避免从头再去做匹配。
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## C++代码
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```
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class Solution {
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public:
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void preKmp(int* next, const string& s){
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next[0] = -1;
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int j = -1;
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for(int i = 1; i < s.size(); i++){
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while (j >= 0 && s[i] != s[j + 1]) {
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j = next[j];
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}
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if (s[i] == s[j + 1]) {
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j++;
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}
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next[i] = j;
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}
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}
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int strStr(string haystack, string needle) {
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if (needle.size() == 0) {
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return 0;
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}
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int next[needle.size()];
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preKmp(next, needle);
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int j = -1;
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for (int i = 0; i < haystack.size(); i++) {
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while(j >= 0 && haystack[i] != needle[j + 1]) {
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j = next[j];
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}
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if (haystack[i] == needle[j + 1]) {
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j++;
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}
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if (j == (needle.size() - 1) ) {
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return (i - needle.size() + 1);
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}
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}
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return -1;
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}
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};
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```
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> 笔者在先后在腾讯和百度从事技术研发多年，利用工作之余重刷leetcode，本文 [GitHub](https://github.com/youngyangyang04/leetcode-master )：https://github.com/youngyangyang04/leetcode-master 已经收录，欢迎star，fork，共同学习，一起进步。
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