KMP模式匹配算法模板

模板1：

#include<bits/stdc++.h>
using namespace std;

void InitNext(char *s, int *next){
    int i = 0, j = -1, len = strlen(s);
    next[0] = -1;
    while(i < len){
        if (j == -1 || s[i] == s[j]){
            ++i;
            ++j;
            next[i] = j;    
        }
        else  j = next[j];
    }
}

int IndexKMP(char T[], char s[], int *next){
    int i = 0, j = -1, l = strlen(s), L = strlen(T);
    InitNext(s, next);
    while(j < l && i < L){
        if (j == -1 || T[i] == s[j]){
            ++i;
            ++j;
        }
        else j = next[j];
    }
    if (j >= l) return i-j+1;
    else return 0;
}

int main()
{
    char T[200], s[20];
    int next[20];
    scanf("%s %s", T, s);
    int ans = IndexKMP(T, s, next);
    cout<<ans<<endl;
    return 0;
}

模板2（大白书）：

#include<bits/stdc++.h>
using namespace std;
const int maxn = 1000 + 10;

void getFail(char* P, int* f) {
    int len = strlen(P);
    f[0] = f[1] = 0;
    for (int i = 1; i < len; ++i) {
        int j = f[i];
        while(j && P[i] != P[j]) j = f[j];
        f[i+1] = P[i] == P[j] ? j + 1 : 0;
    }
}

int find(char* T, char* P, int* f) {
    int len1 = strlen(T), len2 = strlen(P);
    getFail(P, f);
    int j = 0;
    for (int i = 0; i < len1; ++i) {
        while(j && T[i] != P[j]) j = f[j];
        if (T[i] == P[j]) ++j;
        if (j == len2) return i - j + 1;
    }
}

int main() {
    char T[maxn], P[maxn];
    int f[maxn];
    while(cin>>T>>P) {
        cout<<find(T, P, f)<<endl;
    }

    return 0;
}