KMP子串匹配

分为两个操作：

1.求next数组/longestPrefix数组

2.kmp字符串匹配

模板：

#include <iostream>
#include <vector>
#include <string>
using namespace std;

vector<int> computePrefix(string pat) {
    int m = pat.size();
    vector<int> longestPrefix(m);
    for(int i = 1, k = 0; i < m; i ++ ) {
        while(k > 0 && pat[i] != pat[k]) {
            k = longestPrefix[k - 1];
        }   
        if(pat[i] == pat[k]) {
            longestPrefix[i] = ++k;
        } 
        else {
            longestPrefix[i] = k;
        }    
    }
    return longestPrefix;
}

void kmp(string text, string pat) {
    int n = text.size();
    int m = pat.size();
    vector<int> longestPrefix = computePrefix(pat);
       
    for(int i = 0, k = 0; i < n; i ++ ) {
        while(k > 0 && pat[k] != text[i]) {
            k = longestPrefix[k - 1];
        }
        if(pat[k] == text[i]) {
            k ++;
        }
        if(k == m) {
            cout << i - m + 1 + 1 << endl;
            k = longestPrefix[k - 1];
        }
    }
}
int main() {
    string text, pat;
    cin >> text >> pat;

    kmp(text, pat);

    return 0;
}