求助

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 100 + 5;
char mp[N][N];
int f[N][N];
bool vis[N][N];
int n, m;
char d[2] = {'B', 'W'};
void dfs(int x, int y) {
	if (x > n) {
		for (int i = 1; i <= n; ++i) {
			for (int j = 1; j <= m; ++j)
				cout << mp[i][j];
			cout << endl;
		}
	//	return;
		exit(0);
	}
	if (y > m) {
		dfs(x + 1, 1);
		return;
	}
	if (mp[x][y] == '-') {
		dfs(x, y + 1);
		return;
	}
	for (int i = 0; i < 2; ++i) {
		if (mp[x - 1][y] == d[i] || mp[x][y - 1] == d[i]) continue;
		mp[x][y] = d[i];
		dfs(x, y + 1);
		mp[x][y] = '.';
	}
}
int main()
{
	int i, j;
	cin >> n >> m;
	for (i = 1; i <= n; ++i)
		for (j = 1; j <= m; ++j)
			cin >> mp[i][j];
	dfs(1, 1);
				
	return 0;
}
/*
5 4 
....
....
....
....
....

2 4
--.-
....
*/