Zig-zag

Write a program that reads several matrices of integer numbers, and that for each one tells whether the result of traversing it in zig-zags is a strictly increasing sequence. We must start at the top-left position, go down the first column, up the second column, down the third column, and so on.

Input

Input consists of several matrices, each with the number of rows $r \ge 1$ and the number of columns $c \ge 1$ , followed by $r$ rows with $c$ integer numbers each.

Output

For every matrix, print its number followed by either “yes” o “no”, depending on whether the zig-zag traversal of the matrix generates a strictly increasing sequence or not.

Problem information

Author: Unknown
Translator: Salvador Roura

Generation: 2026-01-25T11:39:53.943Z