Program to rotate a matrix by 90 degree clockwise.

Question :

You have to rotate the matrix by 90 degrees.

For example if you have

[1][2][3][4]
[5][6][7][8]
[9][0][1][2]
[3][4][5][6]

output must be

[3][9][5][1]
[4][0][6][2]
[5][1][7][3]
[6][2][8][4] 

Solution : 

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package Matrices;   import java.util.Arrays;   /**  * Created by Aniket on 1/26/14.  */ public class NinetyDegRotator {       public static int [][] rotate(int [][] matrix){         int rows = matrix.length;         int cols = matrix[0].length;         int [][] rotatedMatrix = new int[rows][cols];         for(int i =0; i<rows;i++){             for(int j=0;j<cols;j++){                 rotatedMatrix[i][j] = matrix[cols-j-1][i];             }         }         return rotatedMatrix;     }       public static void twoDArrayPrinter(int [][] matrix){           for(int []array : matrix){             System.out.println(Arrays.toString(array));         }       }       public static void main(String args[]){           int [][] matrix = new int[][]{                 {1,2,3,4},                 {5,6,7,8},                 {9,0,1,2},                 {3,4,5,6}         };           System.out.println("Original Array : ");         NinetyDegRotator.twoDArrayPrinter(matrix);         int [][] rotatedMatrix = ninetyDegRotator.rotate(matrix);         System.out.println("Rotated Array : ");         NinetyDegRotator.twoDArrayPrinter(rotatedMatrix);     }   }

Output :

Original Array :
[1, 2, 3, 4]
[5, 6, 7, 8]
[9, 0, 1, 2]
[3, 4, 5, 6]
Rotated Array :
[3, 9, 5, 1]
[4, 0, 6, 2]
[5, 1, 7, 3]
[6, 2, 8, 4]

Note : Above algorithm takes O(N^2) time complexity.

 To make the transformation in place it has to be a square matrix(n*n)

Code :

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package Matrices;   /**  * Created by Aniket on 1/26/14.  */ public class TransposeCreator {     public static void inPlaceTranspose(int [][] matrix){           int rows = matrix.length;         int cols = matrix[0].length;           for(int i=0;i<rows;i++){             for(int j=i+1;j<cols;j++){                 matrix[i][j] = matrix[i][j] + matrix[j][i];                 matrix[j][i] = matrix[i][j] - matrix[j][i];                 matrix[i][j] = matrix[i][j] - matrix[j][i];             }         }     }       public static int[][] transpose(int[][] matrix){           int rows = matrix.length;         int cols = matrix[0].length;           int[][] transposedMatrix = new int[cols][rows];           for(int i=0;i<cols;i++){             for(int j=0;j<rows;j++){                 transposedMatrix[i][j] = matrix[j][i];             }         }           return transposedMatrix;       }       public static void inPlaceRowsSwapper(int [][] matrix){         int rows = matrix.length;         int cols = matrix[0].length;           for(int i=0;i<rows;i++){             for(int j=0;j<cols/2;j++){                 matrix[i][j] = matrix[i][j] + matrix[i][cols-j-1];                 matrix[i][cols-j-1] = matrix[i][j] - matrix[i][cols-j-1];                 matrix[i][j] = matrix[i][j] - matrix[i][cols-j-1];             }         }       }         public static void main(String args[]){           int [][] matrix = new int[][]{                 {1,2,3,4},                 {5,6,7,8},                 {9,0,1,2},                 {3,4,5,6}         };           System.out.println("Original Array : ");         NinetyDegRotator.twoDArrayPrinter(matrix);         System.out.println("Transposed Matrix");         NinetyDegRotator.twoDArrayPrinter(TransposeCreator.transpose(matrix));         TransposeCreator.inPlaceTranspose(matrix);         System.out.println("InPlace Transposed matrix");         NinetyDegRotator.twoDArrayPrinter(matrix);         System.out.println("90deg rotation matrix");         TransposeCreator.inPlaceRowsSwapper(matrix);         NinetyDegRotator.twoDArrayPrinter(matrix);       } }

Output :

Original Array :
[1, 2, 3, 4]
[5, 6, 7, 8]
[9, 0, 1, 2]
[3, 4, 5, 6]
Transposed Matrix
[1, 5, 9, 3]
[2, 6, 0, 4]
[3, 7, 1, 5]
[4, 8, 2, 6]
InPlace Transposed matrix
[1, 5, 9, 3]
[2, 6, 0, 4]
[3, 7, 1, 5]
[4, 8, 2, 6]
90deg rotation matrix
[3, 9, 5, 1]
[4, 0, 6, 2]
[5, 1, 7, 3]
[6, 2, 8, 4]