Cracking the Coding Interview Q1.6

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Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

 

思路：從最晚層向內，一層一層交換。

 

    public static void rotate(int[][] matrix, int n) {        for (int layer = 0; layer < n / 2; ++layer) {            int first = layer;            int last = n - 1 - layer;            for(int i = first; i < last; ++i) {                int offset = i - first;                int top = matrix[first][i]; // save top                // left -> top                matrix[first][i] = matrix[last-offset][first];                             // bottom -> left                matrix[last-offset][first] = matrix[last][last - offset];                 // right -> bottom                matrix[last][last - offset] = matrix[i][last];                 // top -> right                matrix[i][last] = top; // right <- saved top            }        }    }