Rotate matrix by 90 degree

Rotate matrix by 90 degree OR
Turn an 2D array by 90 degree OR
Rotate a two dimensional array OR
Given N*M matrix, rotate it by 90 degree to left and right.

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Given N*M Matrix, Rotate it by 90 degrees.
 
Lets understand the problem statement graphically and it will be more clear,  

Lets see given input and expected output below,

Algorithm

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 There are 2 ways to Rotate a Matrix by 90 degrees

1. In Place.
2. Using extra Memory.

We already saw how to Rotate a Matrix In-Place: Rotate Matrix to 90 degrees Inplace.

In this post, we will focus on Rotating a Matrix by 90 degrees clockwise using Extra memory.

For Rotating a matrix to 90 degrees clockwise, We need to transform each row of a Matrix to a column in rotated matrix. (Check the rotated matrix image above)

It is very easy to solve this problem if it is well understood.  

What will be Rows and Columns of Rotated Result Matrix?
For rotating matrix to 90 degrees, we need to transform rows into columns and columns to rows in a result matrix. So number of rows in rotated matrix will be equal to number of columns of original matrix and number of columns in rotated matrix will be equal to number of rows.

int[][] rotatedMatrix = new int[colsOfOriginalMatrix][rowsOfOriginalMatrix]

So to summarize our Algorithm:

1. First row of original Matrix will be last column of Rotated Matrix.
2. Second row of original Matrix will be second last column of Rotated Matrix.
3. Third row of original Matrix will be third last column of Rotated Matrix.
   and so on.

You may like to check our popular post on Matrix questions,

1. Top 10 Matrix Interview Questions in Java
   
2. Print Matrix Diagonally OR Diagonal order of Matrix.
   
3. Transpose of Matrix Inplace
   

Java Program to Rotate a Matrix by 90 degrees

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package javabypatel;

public class RotateMatrix {

 public static void main(String[] args) {
  new RotateMatrix();
 }

 public RotateMatrix() {
  int[][] matrix = {
    {1,  2,  3,  4},
    {5,  6,  7,  8},
    {9,  10, 11, 12},
    {13, 14, 15, 16},
    {17, 18, 19, 20}
  };

  System.out.println("Original Matrix :");
  printMatrix(matrix);

  int[][] rotatedMatrix = rotateMatrixBy90DegreeCounterClockwise(matrix);
  System.out.println("Rotated Matrix :");
  printMatrix(rotatedMatrix);
 }

 //Rotate Matrix to 90 degree toward Right(clockwise)
 private int[][] rotateMatrixBy90DegreeClockwise(int[][] matrix) {

  int totalRowsOfRotatedMatrix = matrix[0].length; //Total columns of Original Matrix
  int totalColsOfRotatedMatrix = matrix.length; //Total rows of Original Matrix

  int[][] rotatedMatrix = new int[totalRowsOfRotatedMatrix][totalColsOfRotatedMatrix];

  for (int i = 0; i < matrix.length; i++) {
   for (int j = 0; j < matrix[0].length; j++) {
    rotatedMatrix[j][ (totalColsOfRotatedMatrix-1)- i] = matrix[i][j]; 
   }
  }
  return rotatedMatrix;
 }

 //Rotate Matrix to 90 degree toward Left(counter clockwise)
 private int[][] rotateMatrixBy90DegreeCounterClockwise(int[][] matrix) {

  int totalRowsOfRotatedMatrix = matrix[0].length; //Total columns of Original Matrix
  int totalColsOfRotatedMatrix = matrix.length; //Total rows of Original Matrix

  int[][] rotatedMatrix = new int[totalRowsOfRotatedMatrix][totalColsOfRotatedMatrix];

  for (int i = 0; i < matrix.length; i++) {
   for (int j = 0; j < matrix[0].length; j++) {
    rotatedMatrix[(totalRowsOfRotatedMatrix-1)-j][i] = matrix[i][j]; 
   }
  }
  return rotatedMatrix;
 }

 private static void printMatrix(int[][] matrix){
  for (int i = 0; i < matrix.length; i++) {
   for (int j = 0; j < matrix[0].length; j++) {
    System.out.print(matrix[i][j] + "   "); 
   }
   System.out.println();
  }
 }
}

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Rotate Matrix by 90 degrees clockwise Inplace

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Enjoy !!!! 

If you find any issue in post or face any error while implementing, Please comment.