KMP

#include 
using namespace std;
const int N = 1e5 + 10, M = 1e6 + 10;
char s[M], p[N];
int n, m, ne[N];
int main(){
	cin >> n >> p + 1 >> m >> s + 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;
	}
	for (int i = 1, j = 0; i <= m; ++ i){
		while (j && s[i] != p[j + 1]) j = ne[j];
		if (s[i] == p[j + 1]) ++ j;
		if (j == n){
			cout << i - n << " ";
			j = ne[j];
		}
	}
	return 0;
}

Acwing模板：https://www.acwing.com/problem/content/833/