Problem 512. Spot the rectangle

Created by Ned Gulley

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This problem is related to the 17x17 challenge. Given a matrix filled with ones and zeros, determine whether or not any rectangles are present. A rectangle is a formed whenever four ones appear in the corners of a rectangular region of the matrix.
Examples:
 Input  a = [ 1 0 0 0 0
              0 0 0 1 0
              0 0 0 0 1
              0 0 0 0 1
              0 0 1 0 0 ]
 Output tf is false
You can't form any rectangles here.
 Input  a = [ 1 0 1 0
              0 0 1 0
              1 0 1 0
              0 0 1 1 ]
 Output tf is true
There is a rectangle: a([1 3],[1 3]) is [1 1; 1 1]

Solve

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Last Solution submitted on Oct 31, 2025

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rifat on 15 Jun 2014

test cases imply that the question title should be "spot the square"

Ned Gulley on 14 Jan 2015

I added a rectangular (non-square) test case. Thanks for the note.

Christian Schröder on 28 Sep 2022

Could you add

a = ones(3) - eye(3)

to the test suite?

Abdelrahman Adel on 7 Apr 2024

It was a good problem.
If anyone find it's difficult , you can download my answer
http://up-4.net/d/tt5L

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Problem 512. Spot the rectangle

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Problem 512. Spot the rectangle

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Last 200 Solutions

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Problem Recent Solvers160

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