It’s been a while since I’ve written a blog about a technical problem I’ve solved. The truth is I haven’t been grinding on HackerRank or LeetCode as much as I used to, and all of my time has been spent working on projects.

That changed this week. Today’s problem took me a long time to solve, longer than I’d like to admit, but provided a great opportunity to shake out the cobwebs and get back on that LeetCode grind. The solution I came up with meets the O(1) space complexity requirement, and runs in O(n * log n) time complexity (I think).

I’d also like to mention that I found CodeSignal recently, and I have been enjoying it so far. I only just started their Interview Practice track, but the UI is a step up from LeetCode/HackerRank, their feature sets and test cases are solid, and the amount of information given for each problem has been good. Check it out if you need a change of scenery.

So, let’s get solving.

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THE PROBLEM

Here is a link to the problem on Code Signal

You are given an n x n 2D matrix that represents an image. Rotate the image by 90 degrees (clockwise).

Note: Try to solve this task in-place (with O(1) additional memory), since this is what you’ll be asked to do during an interview.
Constraints:
  1 ≤ a.length ≤ 100
  a[i].length = a.length
  1 ≤ a[i][j] ≤ 104
Input/Output:
  [execution time limit] 4 seconds (js)
  [input] array.array.integer a
  [output] array.array.integer

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THE TESTS

Test #1
	Input:
	[[1]]

	Output:
	[[1]]

	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	Test #2
	Input:
	[[1,2,3],
	 [4,5,6],
	 [7,8,9]]

	Output:
	[[7,4,1],
	 [8,5,2],
	 [9,6,3]]

	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	Test #3
	Input:
	[[6,3,1,7],
	 [8,2,4,5],
	 [1,6,2,9],
	 [5,7,3,4]]

	Output:
	[[5,1,8,6],
	 [7,6,2,3],
	 [3,2,4,1],
	 [4,9,5,7]]

	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	Test #4
	Input:
	[[10,9,6,3,7],
	 [6,10,2,9,7],
	 [7,6,3,8,2],
	 [8,9,7,9,9],
	 [6,8,6,8,2]]

	Output:
	[[6,8,7,6,10],
	 [8,9,6,10,9],
	 [6,7,3,2,6],
	 [8,9,8,9,3],
	 [2,9,2,7,7]]

	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	Test #5
	Input:
	[[40,12,15,37,33,11,45,13,25,3],
	 [37,35,15,43,23,12,22,29,46,43],
	 [44,19,15,12,30,2,45,7,47,6],
	 [48,4,40,10,16,22,18,36,27,48],
	 [45,17,36,28,47,46,8,4,17,3],
	 [14,9,33,1,6,31,7,38,25,17],
	 [31,9,17,11,29,42,38,10,48,6],
	 [12,13,42,3,47,24,28,22,3,47],
	 [38,23,26,3,23,27,14,40,15,22],
	 [8,46,20,21,35,4,36,18,32,3]]

	Output:
	[[8,38,12,31,14,45,48,44,37,40],
	 [46,23,13,9,9,17,4,19,35,12],
	 [20,26,42,17,33,36,40,15,15,15],
	 [21,3,3,11,1,28,10,12,43,37],
	 [35,23,47,29,6,47,16,30,23,33],
	 [4,27,24,42,31,46,22,2,12,11],
	 [36,14,28,38,7,8,18,45,22,45],
	 [18,40,22,10,38,4,36,7,29,13],
	 [32,15,3,48,25,17,27,47,46,25],
	 [3,22,47,6,17,3,48,6,43,3]]

	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#austin-smith #programming #codesignal #rotate-image-matrix #javascript