Problems
Checking for an undirected graph
Checking for an undirected graph
For a given square matrix n x n of zeros and ones determine whether it can be the adjacency matrix of a simple undirected graph. The simple graph does not contain loops and multiple edges.
Input
The first line contains the value of n (1 ≤ n ≤ 100). Each of the next n lines contains n numbers, describing the adjacency matrix.
Output
Print YES, if the graph is simple undirected and NO otherwise.
Input example #1
3 0 1 1 1 0 1 1 1 0
Output example #1
YES
Input example #2
3 0 1 1 1 0 1 0 1 0
Output example #2
NO