Rotate Image

06/27/2016 Array

Question
Solution

Question

You are given an $n*n$ 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:

Could you do this in-place?

Solution

Result: Accepted Time: 0 ms

Here should be some explanations.

void rotate(int** mat, int rsz, int csz) {
    const int rs = rsz - 1, cs = csz - 1, rs2 = rsz >> 1;
    for(int i = 0, tmp; i < rs2; i++)
        for(int j = i; j < cs - i; j++)
        {
            tmp = mat[i][j];
            mat[i][j] = mat[rs - j][i];
            mat[rs - j][i] = mat[rs - i][cs - j];
            mat[rs - i][cs - j] = mat[j][cs - i];
            mat[j][cs - i] = tmp;
        }
}

Complexity Analytics

Time Complexity: $O(n^2)$
Space Complexity: $O(1)$