实现KMP算法，C++

以下是C++实现的KMP算法：

#include <iostream>
#include <string>
#include <vector>

using namespace std;

void getNext(string s, vector<int>& next) {
    int i = 0, j = -1;
    next[0] = -1;

    while(i < s.length() - 1) {
        if(j == -1 || s[i] == s[j]) {
            i++;
            j++;
            next[i] = j;
        }
        else {
            j = next[j];
        }
    }
}

int kmp(string s1, string s2) {
    vector<int> next(s2.length(), -1);
    getNext(s2, next);

    int i = 0, j = 0;
    while(i < s1.length() && j < s2.length()) {
        if(j == -1 || s1[i] == s2[j]) {
            i++;
            j++;
        }
        else {
            j = next[j];
        }
    }

    if(j == s2.length()) {
        return i - j;
    }

    return -1;
}

int main() {
    string s1 = "hello world";
    string s2 = "world";
    int pos = kmp(s1, s2);
    if(pos != -1) {
        cout << "匹配成功，位置为：" << pos << endl;
    }
    else {
        cout << "匹配失败" << endl;
    }
    return 0;
}

其中，`getNext`函数用于生成模式串`s2`的`next`数组，`kmp`函数用于在文本串`s1`中查找模式串`s2`。若查找成功，返回匹配的位置；否则返回-1。