牛客网——地、颜色、魔法（DFS）

只有75%通过，估计是因为递归调用次数过多导致堆栈溢出。题目如下：

 这是我的代码，想法是从边缘开始涂色为+号，计算+号个数，结果用总个数减去加号个数作为输出：

#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
bool flag[10000][10000];
char map[10000][10000];
int dr[4] = { -1, 0, 1, 0 };
int dc[4] = { 0, 1, 0, -1 };
int ans = 0;
int n,m;

void dfs(int x ,int y)
{
	if (map[x][y] == '#') return;
	for (int i = 0; i < 4; i++)
	{
		if (map[x + dr[i]][y + dc[i]] =='.'&&flag[x + dr[i]][y + dc[i]]==false)
		{
			map[x + dr[i]][y + dc[i]] = '+';
			flag[x + dr[i]][y + dc[i]] = true;
			dfs(x + dr[i], y + dc[i]);
			flag[x + dr[i]][y + dc[i]] = false;
			//map[x + dr[i]][y + dc[i]] = '.';
		}
	}
}


int main(void)
{
	cin >> n >> m;
	for (int i = 0; i <= n + 1; i++)
		for (int j = 0; j <= m + 1; j++)
		{
			map[i][j] = '.';
			flag[i][j] = false;
		}
	for (int i = 1; i <= n; i++)
	{
		for (int j = 1; j <= m; j++)
		{
			cin >> map[i][j];
		}
	}
	for (int i = 0; i < n + 2; i++)
	{
		dfs(0, i);
		dfs(m, i);
	}
	for (int i = 1; i < m + 1; i++)
	{
		dfs(i, 0);
		dfs(i, n);
	}
	for(int i=1;i<=n;i++)
		for (int j = 1; j <= m; j++)
		{
			if (map[i][j] == '+')
				ans++;
		}
	cout << m * n - ans << endl;
	system("pause");
	return 0;
}