Preparing NOJ

Seating of Students

2000ms 262144K


Students went into a class to write a test and sat in some way. The teacher thought: "Probably they sat in this order to copy works of each other. I need to rearrange them in such a way that students that were neighbors are not neighbors in a new seating."

The class can be represented as a matrix with n rows and m columns with a student in each cell. Two students are neighbors if cells in which they sit have a common side.

Let's enumerate students from 1 to n·m in order of rows. So a student who initially sits in the cell in row i and column j has a number (i - 1)·m + j. You have to find a matrix with n rows and m columns in which all numbers from 1 to n·m appear exactly once and adjacent numbers in the original matrix are not adjacent in it, or determine that there is no such matrix.


The only line contains two integers n and m (1 ≤ n, m ≤ 105; n·m ≤ 105) — the number of rows and the number of columns in the required matrix.


If there is no such matrix, output "NO" (without quotes).

Otherwise in the first line output "YES" (without quotes), and in the next n lines output m integers which form the required matrix.

Sample Input:

2 4

Sample Output:

5 4 7 2
3 6 1 8

Sample Input:

2 1

Sample Output:



In the first test case the matrix initially looks like this:

1 2 3 4
5 6 7 8

It's easy to see that there are no two students that are adjacent in both matrices.

In the second test case there are only two possible seatings and in both of them students with numbers 1 and 2 are neighbors.



Provider CodeForces

Origin Codeforces Round #454 (Div. 1, based on Technocup 2018 Elimination Round 4)

Code CF906B


brute forceconstructive algorithmsmath

Submitted 118

Passed 47

AC Rate 39.83%

Date 03/04/2019 16:12:57


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