AcWing4312.出现次数

题目链接

https://www.acwing.com/problem/content/4315/

题目思路

KMP算法,再通过查询子串来计算出现次数

题目代码

#include <iostream>
#include <algorithm>

using namespace std;
const int N = 1010;
int ne[N];
char s[N], p[N];
int n, m, q;

int main()
{
    cin >> n >> m >> q;
    cin >> s + 1 >> p + 1;
    
    for(int i = 2, j = 0; i <= n; i ++ )
    {
        while(j && p[i] != p[j + 1])
            j = ne[j];
        if(p[i] == p[j + 1]) j ++ ;
        ne[i] = j;
    }
    
    while(q -- )
    {
        int l, r; 
        cin >> l >> r;
        int ans = 0;
        for(int i = l, j = 0; i <= r; i ++ )
        {
            while(j && s[i] != p[j + 1]) j = ne[j];
            if(s[i] == p[j + 1]) j ++ ;
            if(j == m)
            {
                ans ++ ;
                j = ne[j];
            }
        } 
        cout << ans << endl;
    }
    return 0;
}