【CodeForces】510B - Fox And Two Dots（bfs）

点击打开题目

B. Fox And Two Dots

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Fox Ciel is playing a mobile puzzle game called "Two Dots". The basic levels are played on a board of size n × m cells, like this:

Each cell contains a dot that has some color. We will use different uppercase Latin characters to express different colors.

The key of this game is to find a cycle that contain dots of same color. Consider 4 blue dots on the picture forming a circle as an example. Formally, we call a sequence of dots d1, d2, ..., dk a cycle if and only if it meets the following condition:

1. These k dots are different: if i ≠ j then di is different from dj.
2. k is at least 4.
3. All dots belong to the same color.
4. For all 1 ≤ i ≤ k - 1: di and di + 1 are adjacent. Also, dk and d1 should also be adjacent. Cells x and y are called adjacent if they share an edge.

Determine if there exists a cycle on the field.

Input

The first line contains two integers n and m (2 ≤ n, m ≤ 50): the number of rows and columns of the board.

Then n lines follow, each line contains a string consisting of m characters, expressing colors of dots in each line. Each character is an uppercase Latin letter.

Output

Output "Yes" if there exists a cycle, and "No" otherwise.

Examples

input

3 4
AAAA
ABCA
AAAA

output

Yes

input

3 4
AAAA
ABCA
AADA

output

No

input

4 4
YYYR
BYBY
BBBY
BBBY

output

Yes

input

7 6
AAAAAB
ABBBAB
ABAAAB
ABABBB
ABAAAB
ABBBAB
AAAAAB

output

Yes

input

2 13
ABCDEFGHIJKLM
NOPQRSTUVWXYZ

output

No

Note

In first sample test all 'A' form a cycle.

In second sample there is no such cycle.

The third sample is displayed on the picture above ('Y' = Yellow, 'B' = Blue, 'R' = Red).

从前到最后进行一次bfs，在每一个点向四周搜索（但是不能走回头路），每搜到一个点就用vis标记一下。

如果搜到了vis标记过的点，而且和这个点是同一种颜色，那么说明肯定打环了，说明就成立。

代码如下：

#include <stdio.h>
#include <cstring>
#include <algorithm>
using namespace std;
#define CLR(a,b) memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
#define LL long long
int h,w;
char mapp[55][55];
bool vis[55][55];
int mx[4] = {0,0,1,-1};
int my[4] = {1,-1,0,0};
bool ans;
void bfs(int x,int y,int fx,int fy)
{
	if (vis[x][y])
	{
		ans = true;
		return;
	}
	vis[x][y] = true;
	int nx,ny;
	for (int i = 0 ; i < 4 ; i++)
	{
		nx = x + mx[i];
		ny = y + my[i];
		if (nx == fx && ny == fy)
			continue;
		if (mapp[nx][ny] == mapp[x][y])
			bfs(nx,ny,x,y);
	}
}
int main()
{
	while (~scanf ("%d %d",&h,&w))
	{
		ans = false;
		for (int i = 1 ; i <= h ; i++)
			scanf ("%s",mapp[i]+1);
		CLR(vis,false);
		for (int i = 1 ; i <= h ; i++)
		{
			for (int j = 1 ; j <= w ; j++)
			{
				if (!vis[i][j])
					bfs(i,j,i,j);
				if (ans)
					break;
			}
			if (ans)
				break;
		}
		printf (ans ? "Yes\n" : "No\n");
	}
	return 0;
}