POJ - 3461 Oulipo——kmp

求模式串在字符串中出现的次数。

统计次数时，要注意当完成一组匹配之后令j = next【j】，以便开启另一组匹配

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;
const int maxn = 1000000 + 10;
int next[maxn], leno, lenp;
char o[maxn], p[maxn];
void NEXT() {
    int i = 0, j = -1;
    next[0] = -1;
    while (i < lenp) {
        if (j == -1 || p[i] == p[j]) {
            i++, j++;
            if (p[i] != p[j]) next[i] = j;
            else next[i] = next[j];
        }
        else j = next[j];
    }
}
void KMP() {
    int i = 0, j = 0, cnt = 0;
    while (i < leno && j < lenp) {
        if (j == -1 || o[i] == p[j]) {
            i++, j++;
        }
        else j = next[j];
        if (j == lenp) {
            j = next[j], cnt++;
        }
    }
    printf("%d\n", cnt);
}
int main() {
    int T; scanf("%d", &T);
    while (T--) {
        scanf("%s%s", p, o);
        leno = strlen(o), lenp = strlen(p);
        NEXT();
        KMP();
    }
    return 0;
}