求dalao指出错误(全WA)

#include<bits/stdc++.h>
using namespace std;
const int N=153;
int d[N][N],k[N][N];
bool mp[N][N];
int ans,n;
void dfs(int i,int j,int a,int b){
	if(b+1<=n&&k[a][b+1]-k[i-1][b+1]==0){
		dfs(i,j,a,b+1);
//		printf("[%d,%d] [%d,%d]\n",i,j,a,b+1);
		ans++;
	}
	if(a+1<=n&&d[a+1][b]-d[a+1][j-1]==0){
		dfs(i,j,a+1,b);
//		printf("[%d,%d] [%d,%d]\n",i,j,a+1,b);
		ans++;
	}
}
int main(){
	char c;
//	ios::sync_with_stdio(0);
	cin>>n;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			cin>>c;
			mp[i][j]=(c=='W'?0:1);
			d[i][j]=d[i][j-1]+mp[i][j];
		}
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			k[i][j]=k[i-1][j]+mp[i][j];
		}
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			if(!mp[i][j]){ans++;dfs(i,j,i,j);}
		}
	}
	cout<<ans<<"\n";
	return 0;
}