翻了一下 $2021$ 年的代码，下了第一个测试点，发现 Windows 输出正确，但是洛谷 WA

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

int n, m, s[500001], g[1001][1001];
bool t[1001][1001];

void dfs(int x, int y, int k, bool ist) {
	if (x <= 0 || x > n || y <= 0 || y > n || ist != t[x][y] || g[x][y] != -1) return;
	++s[k];
	g[x][y] = k;
	dfs(x - 1, y, k, !ist);
	dfs(x + 1, y, k, !ist);
	dfs(x, y - 1, k, !ist);
	dfs(x, y + 1, k, !ist);
}

int main() {
	cin >> n >> m;
	for (int i = 1; i <= n; ++i) {
		getchar();
		for (int j = 1; j <= n; ++j) {
			char ch = getchar();
			if (ch == '1') t[i][j] = true;
			else t[i][j] = false;
			g[i][j] = -1;
		}
		
	}
/*	for (int i = 1; i <= n; ++i) {

		for (int j = 1; j <= n; ++j) cout << t[i][j] << ' ';
		cout << endl;
	}*/
	for (int i = 1; i <= m; ++i) {
		int x, y;
		cin >> x >> y;
		if (g[x][y] != -1) s[i] = s[g[x][y]];
		else dfs(x, y, i, t[x][y]);
	}
	for (int i = 1; i <= m; ++i) cout << s[i] << endl;
}