April 23, 2018 May 19, 2018 6 min reading

Warm-up Challenges Left Rotation

I'm posting about my solutions to the HackerRank challenges as a way to improve my learning, reinforce my knowledge, and establish an understanding of the concepts covered. If I help someone by sharing along the way, even better!

Left Rotation is one of the initial challenges with 'EASY' difficulty.

What's the challenge?

A left rotation operation on an array shifts each array element to the left. For example, if two left rotations are performed on the array [1, 2, 3, 4, 5], the array becomes [3, 4, 5, 1, 2].

Given an array a of n integers and a number, d, of left rotations in the array. Return the updated array to be printed as a single line of integers separated by spaces.

What do we have to do?

A function that returns an array of integers after the left rotations have been performed.

Parameters

• a = an array of integers

• d = number of rotations

Limits

• 1 <= n <= 10 ^ 5
• 1 <= d <= n
• 1 <= a [i] <= 10 ^ 6

Sample Input

1 2 3 4 5
4

Sample Output

5 1 2 3 4

Solution

function leftRotation(a, d) {
	return a.concat(a.splice(0, d));
}

Logic

All the logic is contained in this single line, but we can divide it into three parts:

I first used .splice() to get the first d items in the a[0 - d] array. At the beginning of the challenge, the following limit is informed that defines this logic 1 <= d <= n, that is, I don't need to worry about rotating the matrix to the left more times than the items in the array.

I then used .concat() to concatenate (or merge) what's left of a, or everything after a[d], with what I separated in the first step a[0 - d].

And then I finish the function by returning this newly sorted array.

Extra Solutions

Other languages that I speak

Ruby

def leftRotation(a, d)
	a.rotate(d)
end

PYTHON 2 & 3

def leftRotation(a, d):
	return a[a:] + a[:a]

GOLANG

func leftRotation(a[] int32, d int32) []int32 {
	return append(a[d:], a[:d]...)
}

SCALA

def leftRotation(a: Array[Int], d: Int): Array[Int] = {
	return a.drop(d)++a.take(d);
}

JAVA 7 & 8

static int leftRotation(int[] a, int d) {
	int[] rotated = new int[a.length];
	for (int i = 0; i <  a.length; i++) {
				rotated[(i + a.length - d) % a.length] = a[i];
	}
	return rotated;
}

PHP

function leftRotation($a, $d) {
	return array_merge(array_splice($a, $d, count($a)), array_splice($a, 0, $d));
}

Thought: We can judge the heart of a man by his treatment of animals.