48-medium-Rotate_Image.js

/**
48. Rotate Image
You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Note:
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:

Given input matrix =
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

rotate the input matrix in-place such that it becomes:
[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]
Example 2:

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

rotate the input matrix in-place such that it becomes:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]
 */

/**
 * @param {number[][]} matrix
 * @return {void} Do not return anything, modify matrix in-place instead.
 */
var rotate = function (matrix) {
  if (!matrix.length) return [];
  var matrixStr = matrix.reduce((a, b) => a.concat(b), []);
  var arrLen = matrix.length;
  for (var i = 0; i < matrixStr.length; i++) {
    matrix[i % arrLen][arrLen - 1 - Math.floor(i / arrLen)] = matrixStr[i]
  }
};

rotate([
  [5, 1, 9, 11],
  [2, 4, 8, 10],
  [13, 3, 6, 7],
  [15, 14, 12, 16]
])