CODEWITHSUNDEEP
javamatrix
DramaticChapter
DramaticChapter

Reputation: 1

how to rotate a sub-matrix NxN by 90 degree clockwise in a bigger AxB matrix - in Java

everyone ! I'm trying to rotate sub-matrix NxN for 90 degree clockwise within a bigger AxB matrix. Most answers I found is only dealt with a whole matrix NxN. Below is the example.

Given a A x B matrix rotate a sub-matrix NxN for 90 degree clockwise.

Sample input given [3 x 4] matrix rotate sub-matrix [3 x 3] for 90 degree clockwise.

 0  [1  2  3 ]  4
 5  [6  7  8 ]  9
 10 [11 12 13] 14

Expected output

 0  [11  6  1]  4
 5  [12  7  2]  9
 10 [13  8  3] 14

Really appreciate if someone can help me out. Thanks !

Upvotes: 0

Views: 286

Answers (1)

user4910279
user4910279

Reputation:

Try this.

top and left are the coordinates of the upper left corner of the submatrix. n is the size of the submatrix.

static int[][] rotate(int[][] a, int top, int left, int n) {
    int height = a.length, width = a[0].length;
    int[][] b = new int[height][];
    for (int x = 0; x < height; ++x)
        b[x] = Arrays.copyOf(a[x], width);
    for (int x = top, xmax = top + n, ty = left + n - 1; x < xmax; ++x, --ty)
        for (int y = left, ymax = left + n, tx = 0; y < ymax; ++y, ++tx)
            b[tx][ty] = a[x][y];
    return b;
}

And

int[][] a = {
    {0, 1, 2, 3, 4},
    {5, 6, 7, 8, 9},
    {10, 11, 12, 13, 14},
};
int[][] b = rotate(a, 0, 1, 3);
for (int[] row : b)
    System.out.println(Arrays.toString(row));

output:

[0, 11, 6, 1, 4]
[5, 12, 7, 2, 9]
[10, 13, 8, 3, 14]

Upvotes: 1

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