Fox And Two Dots

2000ms

262144K

Description:

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:

$\text{[math]}$

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, ..., d_k a cycle if and only if it meets the following condition:

These k dots are different: if i ≠ j then d_i is different from d_j.
k is at least 4.
All dots belong to the same color.
For all 1 ≤ i ≤ k - 1: d_i and d_i + 1 are adjacent. Also, d_k 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.

Sample Input:

3 4
AAAA
ABCA
AAAA

Sample Output:

Yes

Sample Input:

3 4
AAAA
ABCA
AADA

Sample Output:

No

Sample Input:

4 4
YYYR
BYBY
BBBY
BBBY

Sample Output:

Yes

Sample Input:

7 6
AAAAAB
ABBBAB
ABAAAB
ABABBB
ABAAAB
ABBBAB
AAAAAB

Sample Output:

Yes

Sample Input:

2 13
ABCDEFGHIJKLM
NOPQRSTUVWXYZ

Sample 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).

Informação

Provedor Codeforces

Código CF510B