48. Rotate Image

Problem

Tags: Array, Math, Matrix

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

Code

JS

// 48. Rotate Image (3/26/53841)
// Runtime: 68 ms (67.56%) Memory: 39.11 MB (94.98%) 

/**
 * @param {number[][]} matrix
 * @return {void} Do not return anything, modify matrix in-place instead.
 */
function rotate(matrix) {
    let size = matrix.length,
        level = 0;
    
    while(size > 0) {
        for(let i = level; i < level + size - 1; i++) {
            const top = matrix[level][i]; // go right
            const right = matrix[i][level + size - 1]; // go down
            const bottom = matrix[level + size - 1][level + size - 1 - (i - level)]; // go left
            const left = matrix[level + size - 1 - (i - level)][level]; // go up
            
            matrix[level][i] = left;
            matrix[i][level + size - 1] = top;
            matrix[level + size - 1][level + size - 1 - (i - level)] = right;
            matrix[level + size - 1 - (i - level)][level] = bottom;
        }
        
        level++;
        size -= 2;
    }
};