LeetCode-in-All

48. Rotate Image

Medium

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]

Output: [[7,4,1],[8,5,2],[9,6,3]]

Example 2:

Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]

Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]

Constraints:

• n == matrix.length == matrix[i].length
• 1 <= n <= 20
• -1000 <= matrix[i][j] <= 1000

Solution

#include <stdio.h>

void rotate(int** matrix, int matrixSize, int* matrixColSize) {
    int n = matrixSize;

    for (int i = 0; i < n / 2; i++) {
        for (int j = i; j < n - i - 1; j++) {
            // Defining the four positions to be rotated in a cycle
            int pos[4][2] = {
                {i, j},
                {j, n - 1 - i},
                {n - 1 - i, n - 1 - j},
                {n - 1 - j, i}
            };

            // Starting the cycle rotation
            int t = matrix[pos[0][0]][pos[0][1]];
            for (int k = 1; k < 4; k++) {
                int temp = matrix[pos[k][0]][pos[k][1]];
                matrix[pos[k][0]][pos[k][1]] = t;
                t = temp;
            }
            matrix[pos[0][0]][pos[0][1]] = t;
        }
    }
}

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