https://leetcode-cn.com/problems/spiral-matrix/
点击查看【bilibili】

题目

给定一个包含 m x n 个元素的矩阵（m 行, n 列），请按照顺时针螺旋顺序，返回矩阵中的所有元素。

示例

输入:
[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
输出: [1,2,3,6,9,8,7,4,5]

输入:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
输出: [1,2,3,4,8,12,11,10,9,5,6,7]

解答

1.如果数组为空,返回空数组
2.定义4个边界以及当前方向(direction)
3.当左边界小于等于右边界,且上边界小等于下边界时,执行 while循环:
按照右,下,左,上的顺序,依欠将路径上的字符添加到结果里
4. while循环结束后,返回结果


为什么left<=right && top <= bottom ?
考虑边界问题

答案

var spiralOrder = function (matrix) {
  if (matrix.length === 0) return [];
  let left = 0
  let right = matrix[0].length - 1
  let top = 0
  let bottom = matrix.length - 1
  let direction = 'right'
  let result = []
  /**
   [ 1, 2, 3 ],
   [ 4, 5, 6 ],
   [ 7, 8, 9 ]
   */
  while (left <= right && top <= bottom) {
    if (direction === 'right') {
      for (let i = left; i <= right; i++) {
        result.push(matrix[top][i])
      }
      top++
      direction = 'down'
    } else if (direction === 'down') {
      for (let i = top; i <= bottom; i++) {
        result.push(matrix[i][right])
      }
      right--
      direction = 'left'
    } else if (direction === 'left') {
      for (let i = right; i >= left; i--) {
        result.push(matrix[bottom][i])
      }
      bottom--
      direction = 'top'
    } else if (direction === 'top') {
      for (let i = bottom; i >= top; i--) {
        result.push(matrix[i][left])
      }
      left++
      direction = 'right'
    }
  }
  return result
};