matrix_rotation.go

// Package matrix_rotation contains the solution for HackerRank challenge
// https://www.hackerrank.com/challenges/matrix-rotation-algo/problem.
package matrix_rotation

import (
	"fmt"
	"math"
)

// MatrixRotation prints matrix after rotating its elements anticlockwise r times.
func MatrixRotation(matrix [][]int32, r int32) {
	rows := len(matrix)
	cols := len(matrix[0])

	l := int(math.Round(math.Min(float64(rows), float64(cols))) / 2.0)

	for i := 0; r > 0 && i < l; i++ {
		layer := make([]int32, 2*(rows-2*i+cols-2*i-2))
		rot := int(r) % len(layer)
		if rot == 0 {
			continue
		}

		// Walk the matrix clockwise starting from top left and collect the values
		// for each layer.

		c := 0

		// top left to top right
		for j := i; j < cols-i-1; j++ {
			layer[c] = matrix[i][j]
			c++
		}
		// top right to bottom right
		for j := i; j < rows-i-1; j++ {
			layer[c] = matrix[j][cols-i-1]
			c++
		}
		// bottom right to bottom left
		for j := cols - i - 1; j > i; j-- {
			layer[c] = matrix[rows-i-1][j]
			c++
		}
		// bottom left to top left
		for j := rows - i - 1; j > i; j-- {
			layer[c] = matrix[j][i]
			c++
		}

		// Left shift values.
		layer = append(layer[rot:], layer[:rot]...)

		// Populate the matrix with the values from layer.

		c = 0

		// top left to top right
		for j := i; j < cols-i-1; j++ {
			matrix[i][j] = layer[c]
			c++
		}
		// top right to bottom right
		for j := i; j < rows-i-1; j++ {
			matrix[j][cols-i-1] = layer[c]
			c++
		}
		// bottom right to bottom left
		for j := cols - i - 1; j > i; j-- {
			matrix[rows-i-1][j] = layer[c]
			c++
		}
		// bottom left to top left
		for j := rows - i - 1; j > i; j-- {
			matrix[j][i] = layer[c]
			c++
		}
	}

	// Print the matrix.
	for i := 0; i < rows; i++ {
		for j := 0; j < cols; j++ {
			fmt.Print(matrix[i][j])
			if j < cols-1 {
				fmt.Print(" ")
			}
		}
		fmt.Print("\n")
	}
}