Rotate Image

Problem Description

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 (JavaScript)

/**
 * @param {number[][]} matrix
 * @return {void} Do not return anything, modify matrix in-place instead.
 */
var rotate = function(matrix) {
    const len = matrix.length;
    const half = Math.floor(len/2);
    let tmp;
    
    for(let i = 0; i < len; i++){
        for(let j = 0; j < half; j++){
            tmp = matrix[i][j];
            matrix[i][j] = matrix[i][len-1-j];
            matrix[i][len-1-j] = tmp;
        }
    }
    
    for(let i = 0; i < len; i++){
        for(let j = 0; j < len; j++){
            if(i + j < len - 1){
                tmp = matrix[i][j];
                matrix[i][j] = matrix[len-1-j][len-1-i];
                matrix[len-1-j][len-1-i] = tmp;
            }
        }
    }
};