POJ 3461 Oulipo（KMP裸）

题目链接：点击打开链接

题意：给两个串 求一个串在另一个串中出现的次数。

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <cstring>
#include <cmath>
#include <vector>#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <cstring>
#include <cmath>
#include <vector>
#include <map>
#include <queue>
#include <deque>
#include <stack>

using namespace std;
typedef long long ll;
const int maxn = 1000000+5;
int next[maxn];
char s[maxn],a[maxn];
void cal_next(char *a){
    memset(next,-1,sizeof(next));
    int len = strlen(a);
    int k = -1 ;
    next[0]=-1;
    for(int p = 1 ; p < len ; p++){
        while(k>-1&&a[p]!=a[k+1]) k = next[k];
        if(a[k+1]==a[p]) next[p]=++k;
    }
}
int kmp(char *s,char *a){
    int slen = strlen(s);
    int alen = strlen(a);
    int k = -1;
    int cnt = 0;
    for(int i = 0 ; i < slen ; i++){
        while(k>-1&&a[k+1]!=s[i]) k = next[k];
        if(a[k+1]==s[i]) k++;
        if(k == alen - 1){
            cnt++;
            k=next[k];//效率更高
        }
    }
    return cnt;
}
int main(){
    int kase;
    scanf("%d",&kase);
    while(kase--){
        scanf("%s",a);
        scanf("%s",s);
        cal_next(a);
        printf("%d\n",kmp(s,a));
    }
}