Rotate a 2d n x n matrix IN PLACE

rotate.js

/**
 * @param {number[][]} matrix
 * @return {void} Do not return anything, modify matrix in-place instead.
 */

// Faster than 80.52% of submissions, less than 40.77% memory usage than other submissions

const rotate = function(matrix) {
    const len = matrix.length
    
    // Start with this:
    
    // [1,2,3]
    // [4,5,6]
    // [7,8,9]
    
    for (let j = len - 1; j >= 0; j--) {
        for (let i = j - 1; i >= 0; i--) {
            matrix[j].push(matrix[i].pop())
        }
    }
  
    // Now it's this:
  
    // [ 1 ]
    // [ 4, 5, 2 ]
    // [ 7, 8, 9, 6, 3 ] 
    
    for (let j = 0; j < len - 1; j++) {
        for (let i = j + 1; i < len; i++) {
            matrix[j].unshift(matrix[i].shift())
        }
    }
  
    // After final nested for loop, it's this:
  
    // [7,4,1]
    // [8,5,2]
    // [9,6,3]
  
    
};