字符串KMP || POJ 3461 Oulipo

Posted 2020-10-23 pinkglightning

 

给两个字符串，问前者在后者中出现了多少次，出现次数可以覆盖

*解法：kmp，理解好next数组的含义，第一次匹配完成后，i不变，j = next[j]即可

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define SZ 10005
#define MAXN 1000005
#define INF 1e9+10
int nxt[SZ];
char s[MAXN], p[SZ];
int slen, plen;//每次都调用strlen会浪费时间
void get_next(char p[])
{
    int i = 0, j = -1;
    nxt[0] = -1;
    while(i < plen - 1)
    {
        if(j == -1 || p[i] == p[j])
        {
            i++;
            j++;
            nxt[i] = j;
        }
        else j = nxt[j];
    }
    return;
}
int kmp(char p[], char s[])
{
    int i = 0, j = 0, cnt = 0;
    while(i < slen && j < plen)
    {
        if(j == -1 || s[i] == p[j])
        {
            i++;
            j++;
        }
        else j = nxt[j];
        if(j == plen)
        {
            cnt++;
            j = nxt[j];
        }
    }
    return cnt;
}
int main()
{
    int T;
    scanf("%d", &T);
    while(T--)
    {
        scanf(" %s %s", p, s);
        plen = strlen(p);
        slen = strlen(s);
        get_next(p);
        int cnt = kmp(p, s);
        printf("%d\n", cnt);
    }
    return 0;
}