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10/12/2023 03:28:28

# Рабочее место участника

## Задачи

983. Grid

Ограничения: время – 1s/2s, память – 16MiB Ввод: input.txt или стандартный ввод Вывод: output.txt или стандартный вывод
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Let M be a grid of n rows and n columns. The rows are numbered from 1 to n and the columns are numbered from 1 to n. A cell (i,\ j) denotes the cell in row i and column j in the grid. Each cell is colored in black or white. Let C_{ij} denote the color of the cell (i,\ j). All cells of the form (i,\ i) for 1\ ≤\ i\ ≤\ n are called diagonal cells.
Swapping rows i and j of the grid M denotes the following action: we swap the values of C_"ik" and C_"jk" for k\ =\ 1,\ 2,\ …,\ n. Swapping two columns is defined analogously.
We say that M is white-colorable if it is possible to swap some of the pairs of rows and some of the pairs of columns (in any sequence) so that, after all the swappings, all the diagonal cells of M are white.
Your task is to write a program that determines whether given grid M is white-colorable.
Input
The first line contains a single positive integer n (n\ ≤\ 1000) – the size of the grid. The i-th line of the following n lines contains n characters C_{ij} (i=1,\ 2,\ …,\ n; j=1,\ 2,\ …,\ n) specifying color pattern of the grid. Character C_{ij} is 'B' or 'W' indicating that the color of cell (i,\ j) is black or white respectively.
Output
Write "YES" if given grid is white-colorable or "NO" otherwise.

Sample Input 1

3
WWW
WBB
WBB


Sample Output 1

NO


Sample Input 2

3
BWB
BWW
WWB


Sample Output 2

YES

Источник: РГУ им. И.Канта, осенний командный турнир, 2007