Problem 55220. Matrix Quadrants

Created by Renee Coetsee

Solve Later

Write a function that takes N as the input, and outputs a matrix whose upper-left (NxN) quadrant contains all ones, the lower-right (NxN) quadrant contains all N's, and zeros everywhere else. For example, if N = 3: 

Solve

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Last Solution submitted on Jan 11, 2026

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Aidan Judge on 29 Nov 2022

Good problem!

Andreea on 16 Jan 2023

function M = foursquare(N)
M = zeros(2*N);
for i=1:length(M)/2
for j=1:length(M)/2
M(i,j)=1;
j=j+1;
end
i=i+1;
end
for i=(length(M)/2)+1:length(M)
for j=(length(M)/2)+1:length(M)
M(i,j)=3;
j=j+1;
end
i=i+1;
end
end
Just wrote that program that gives me the right solution but I don't understand why it won't work.Any suggestions?

Christian Schröder on 17 Jan 2023

@Andreea you're hard-coding the value 3 on the twelfth line; the problem description says that the lower-left quadrant should contain N's instead.

Kshitij Patki on 20 Mar 2025

good one

David on 24 Oct 2025

N=3
A=ones(3)
B=zeros(3)
C=N*ones(3)
M=([A B;B C])

I'm just starting out self learning and to my understanding this code answers the question since i made N an input but it says i did it wrong. i guess i have to use this 'foursquare' function (only seeing it for the first time now). can someone please explain what the function does?

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Problem 55220. Matrix Quadrants

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Problem 55220. Matrix Quadrants

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