54.Spiral Matrix

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

Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

/**
 * @param {number[][]} matrix
 * @return {number[]}
 */
var spiralOrder = function (matrix) {
  const result = [];
  let rowStart = 0;
  let rowEnd = matrix.length - 1;
  let colStart = 0;
  let colEnd = matrix[0].length - 1;

  while (rowStart <= rowEnd && colStart <= colEnd) {
    for (let col = colStart; col <= colEnd; col++) {
      result.push(matrix[rowStart][col]);
    }
    rowStart++;

    for (let row = rowStart; row <= rowEnd; row++) {
      result.push(matrix[row][colEnd]);
    }
    colEnd--;

    if (rowStart <= rowEnd) {
      for (let col = colEnd; col >= colStart; col--) {
        result.push(matrix[rowEnd][col]);
      }
    }
    rowEnd--;

    if (colStart <= colEnd) {
      for (let row = rowEnd; row >= rowStart; row--) {
        result.push(matrix[row][colStart]);
      }
    }
    colStart++;
  }

  return result;
};