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CC-18 :Rotate matrix by 90/180/270/360 degrees.

Description:

Given input int matrix mat, rotate its elements in place (without using an extra matrix) by 90/180/270/360 degrees and return the resultant matrix.

Test cases and expected outputs:

Input Expected outputs
rot=90
mat = {
{7,1,4,1},
{9,9,3,0},
{2,1,4,3},
{6,2,7,9}}
Rotated 90% :
6,2,9,7,
2,1,9,1,
7,4,3,4,
9,3,0,1,
Rot=180
mat = {
{3,1,2,6,7},
{9,3,2,7,1},
{1,0,0,9,3},
{0,3,6,9,2},
{7,2,4,9,1}}
Rotated 180% :
1,9,4,2,7,
2,9,6,3,0,
3,9,0,0,1,
1,7,2,3,9,
7,6,2,1,3,
Rot=270
mat = {
{3,1,2,6,7},
{9,3,2,7,1},
{1,0,0,9,3},
{0,3,6,9,2},
{7,2,4,9,1}}
Rotated 270% :
7,1,3,2,1,
6,7,9,9,9,
2,2,0,6,4,
1,3,0,3,2,
3,9,1,0,7,

Pseudocode:

The java method should accept following input parameters: mat (int square matrix), rot (int with values 90/180/270/360).
If rot = 360, there is nothing to be done as 360 degree rotation results in same matrix, so return mat.
Initialise variable n=mat.length.
To rotate the matrix in place we break down the matrix into squares. There are n/2 squares in a matrix of side n. We will rotate one square at a time using logic described below.
Declare in variables ogTop, ogRIght, ogBottom, ogLeft to hold references to 4 corners of square.
Iterate through mat using a for loop, using variable i as loop counter. Loop variable i will be initialized with value 0 and will iterate through all the matrix’s columns one by one till rIdx < mat.length/2:
Iterate through mat using a for loop, using variable j as loop counter. Loop variable j will be initialized with value i and will iterate through all the matrix’s columns one by one till j < mat[0].length:
Initialize below corner variables based on current square :
ogTop=mat[i][j]; ogRight=mat[j][n-1-i];
ogBottom=mat[n-1-i][n-1-j]; ogLeft=mat[n-1-j][i];
Note the sequence of original square : ogTop, ogRight, ogBottom, OgLeft.
If rotation angle is 90, rotate above original sequence by 1 step and assign to the 4 corners:
mat[i][j]=ogLeft; mat[j][n-1-i]=ogTop;
mat[n-1-i][n-1-j]=ogRight; mat[n-1-j][i]=ogBottom;
If rotation is 180, rotate above original sequence by 2 steps and assign to the 4 corners:
mat[i][j]=ogBottom; mat[j][n-1-i]=ogLeft;
mat[n-1-i][n-1-j]=ogTop; mat[n-1-j][i]=ogRight;
If rotation is 180, rotate above original sequence by 3 steps and assign to the 4 corners:
mat[i][j]=ogRight; mat[j][n-1-i]=ogBottom;
mat[n-1-i][n-1-j]=ogLeft; mat[n-1-j][i]=ogTop;
After above loops complete, mat will be rotated by rot degrees. Return mat.

Code:

public int[][] matRotate(int[][] mat, int rot) throws Exception{
	if (rot==360) {return mat;}
	int n=mat.length;
	int ogTop, ogRight, ogBottom, ogLeft;
	for (int i=0; i < mat.length/2; i++) {
		for (int j=i; j< n-1-i; j++) {
			ogTop=mat[i][j];
			ogRight=mat[j][n-1-i];
			ogBottom=mat[n-1-i][n-1-j];
			ogLeft=mat[n-1-j][i];
			if (rot==90) {
				mat[i][j]=ogLeft; mat[j][n-1-i]=ogTop;
				mat[n-1-i][n-1-j]=ogRight; 	mat[n-1-j][i]=ogBottom;
			} else if (rot==180) {
				mat[i][j]=ogBottom; mat[j][n-1-i]=ogLeft;
				mat[n-1-i][n-1-j]=ogTop; 	mat[n-1-j][i]=ogRight;
			}else if (rot==270) {
				mat[i][j]=ogRight; mat[j][n-1-i]=ogBottom;
				mat[n-1-i][n-1-j]=ogLeft; 	mat[n-1-j][i]=ogTop;
			}
		}
	}	
	return mat;
}

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