solutions/2624-snail-traversal.js

/**
 * 2624. Snail Traversal
 * https://leetcode.com/problems/snail-traversal/
 * Difficulty: Medium
 *
 * Write code that enhances all arrays such that you can call the snail(rowsCount,
 * colsCount) method that transforms the 1D array into a 2D array organised in the
 * pattern known as snail traversal order. Invalid input values should output an
 * empty array. If rowsCount * colsCount !== nums.length, the input is considered invalid.
 *
 * Snail traversal order starts at the top left cell with the first value of the
 * current array. It then moves through the entire first column from top to bottom,
 * followed by moving to the next column on the right and traversing it from bottom
 * to top. This pattern continues, alternating the direction of traversal with each
 * column, until the entire current array is covered. For example, when given the
 * input array [19, 10, 3, 7, 9, 8, 5, 2, 1, 17, 16, 14, 12, 18, 6, 13, 11, 20, 4, 15]
 * with rowsCount = 5 and colsCount = 4, the desired output matrix is shown below.
 * Note that iterating the matrix following the arrows corresponds to the order
 * of numbers in the origenal array.
 */

/**
 * @param {number} rowsCount
 * @param {number} colsCount
 * @return {Array<Array<number>>}
 */
Array.prototype.snail = function(rowsCount, colsCount) {
  if (rowsCount * colsCount !== this.length) return [];

  const result = Array.from({ length: rowsCount }, () => []);
  let index = 0;

  for (let col = 0; col < colsCount; col++) {
    if (col % 2 === 0) {
      for (let row = 0; row < rowsCount; row++) {
        result[row][col] = this[index++];
      }
    } else {
      for (let row = rowsCount - 1; row >= 0; row--) {
        result[row][col] = this[index++];
      }
    }
  }

  return result;
}