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2d array rotation

Posted on 2011-03-23
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Last Modified: 2012-05-11
how to rotate a 2d array (matrix) 90 degrees anticlockwise so:

X =
    1    2    3
    4    5    6
    7    8    9

becomes

Y =
    3    6    9
    2    5    8
    1    4    7
0
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Question by:chudyksg
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3 Comments
 
LVL 40

Expert Comment

by:Gurvinder Pal Singh
ID: 35198684
create another empty array of 3x3 dimension, and follow these steps

pick value at 1,1 and put it at 3,1
pick value at 1,2 and put it at 2,1
pick value at 1,3 and put it at 1,1
pick value at 2,1 and put it at 3,2
pick value at 2,3 and put it at 1,2
pick value at 3,1 and put it at 3,3
pick value at 3,2 and put it at 2,3
pick value at 3,3 and put it at 1,3
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LVL 28

Accepted Solution

by:
rrz earned 2000 total points
ID: 35200226
from
http://stackoverflow.com/questions/42519/how-do-you-rotate-a-two-dimensional-array
public int[][] rotateMatrixLeft(int[][] matrix)
{
    /* W and H are already swapped */
    int w = matrix.length;
    int h = matrix[0].length;   
    int[][] ret = new int[h][w];
    for (int i = 0; i < h; ++i) {
        for (int j = 0; j < w; ++j) {
            ret[i][j] = matrix[j][h - i - 1];
        }
    }
    return ret;
}

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0
 

Expert Comment

by:sinsach
ID: 35205990
This will rotate any matrix 90 degrees anti-clock.

/**
* To rotate the array 90 degrees anti-clock wise. This will rotate square
* and non square matrix.
* 
* @param sourceArray
* @return
*/
public int[][] antiClock90Rotation(int[][] sourceArray) {
	int[][] rotatedArray = new int[sourceArray[0].length][sourceArray.length];
	int positionFactor = rotatedArray.length - 1;
	for (int i = 0; i < rotatedArray.length; i++) {
		for (int j = 0; j < rotatedArray[i].length; j++) {
			int a = i - positionFactor;
			a = (a < 0) ? -a : a;
			rotatedArray[i][j] = sourceArray[j][a];
		}
	}
	return rotatedArray;
}

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