吸氧后 RE 四个点，不吸氧 AC。

#include <bits/stdc++.h>
#define int long long
using namespace std;

constexpr int P = 131, MAXN = 1e6 + 5;
string s, t;
int n, m, p[MAXN], h1[MAXN], h2;
char ans[MAXN]; // 这题栈非得模拟不可
int len;

void get_hash() {
	p[0] = 1;
	for (int i = 1; i <= MAXN - 5; i++) p[i] = p[i - 1] * P;
	for (int i = 0; i < m; i++) h2 = h2 * P + t[i];
}

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(nullptr);
	cin >> s >> t;
	n = s.size(), m = t.size();
	get_hash();
	for (int i = 0; i < n; i++) {
		ans[++len] = s[i];
		h1[len] = h1[len - 1] * P + s[i];
		if (h2 == h1[len] - h1[len - m] * p[m]) len -= m;
	}
	for (int i = 1; i <= len; i++) cout << ans[i];
	cout << '\n';
	
	return 0;
}