本人蒟蒻，WA却不知道问题出在哪里，样例也没过，求助大神

#include<iostream> 
#include<cmath> 
#include<string> 
#include<stdio.h>
#include<algorithm>
#include<iomanip>
using namespace std;
int s[21][21];
bool flag(int x, int y, int a, int b) {
	if (x == a + 1 && y == b - 2) return true;
	if (x == a + 2 && y == b - 1) return true;
	if (x == a + 2 && y == b + 1) return true;
	if (x == a + 1 && y == b + 2) return true;
	if (x == a - 1 && y == b + 2) return true;
	if (x == a - 2 && y == b + 1) return true;
	if (x == a - 2 && y == b - 1) return true;
	if (x == a - 1 && y == b - 2) return true;
	return false;
}
int main() {
	int n, m, a, b;
	cin >> n >> m >> a >> b;
	for (int i = 1; i <= n; i++) {
		s[1][i] = 1;
		if (flag(1, i, a, b)) s[1][i] = 0;
	}
	for (int i = 1; i <= m; i++) {
		s[i][1] = 1;
		if (flag(i, 1, a, b)) s[i][1] = 0;
	}
	for (int i = 2; i <= n; i++) {
		for (int j = 2; j <= m; j++) {
			if (flag(i, j, a, b)) {
				s[i][j] = 0;
				continue;
			}
			s[i][j] = s[i - 1][j] + s[i][j - 1];
		}
	}
	/*for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= m; j++) {
			cout << s[i][j] << ' ';
		}
		cout << endl;
	}*/
	cout << s[n][m];
	return 0;
}