时间轴

2025-10-06

init

题目：

P28 找出字符串中第一个匹配项的下标

https://leetcode.cn/problems/find-the-index-of-the-first-occurrence-in-a-string/description/?envType=study-plan-v2&envId=top-interview-150

这题考察 KMP 的

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class Solution {
public:
    int strStr(string s, string p) {
        int n = s.size(), m = p.size();
        if(m == 0) return 0;
        //设置哨兵
        s.insert(s.begin(),' ');
        p.insert(p.begin(),' ');
        vector<int> next(m + 1);
        //预处理next数组
        for(int i = 2, j = 0; i <= m; i++){
            while(j and p[i] != p[j + 1]) j = next[j];
            if(p[i] == p[j + 1]) j++;
            next[i] = j;
        }
        //匹配过程
        for(int i = 1, j = 0; i <= n; i++){
            while(j and s[i] != p[j + 1]) j = next[j];
            if(s[i] == p[j + 1]) j++;
            if(j == m) return i - m;
        }
        return -1;
    }
};


可以直接用 C++的 string.find 函数

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#include <string>
using std::string;

class Solution {
public:
  int strStr(string haystack, string needle) { return haystack.find(needle); }
};