59. Spiral Matrix II

Problem:

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

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

Solution:

Straight-forward.

/**
 * @param {number} n
 * @return {number[][]}
 */
let generateMatrix = function (n) {
  const matrix = [...new Array(n)].map(() => []);
  const halfN = ((n + 1) / 2) | 0;
  let count = 1;
  for (let start = 0; start < halfN; start++) {
    const end = n - start - 1;
    for (let col = start; col <= end; col++) {
      matrix[start][col] = count++;
    }
    for (let row = start + 1; row <= end; row++) {
      matrix[row][end] = count++;
    }
    for (let col = end - 1; col >= start; col--) {
      matrix[end][col] = count++;
    }
    for (let row = end - 1; row > start; row--) {
      matrix[row][start] = count++;
    }
  }
  return matrix;
};

☆: .｡. o(≧▽≦)o .｡.:☆☆: .｡. o(≧▽≦)o .｡.:☆☆: .｡. o(≧▽≦)o .｡.:☆

☆: .｡. o(≧▽≦)o .｡.:☆☆: .｡. o(≧▽≦)o .｡.:☆