22 -【leetcode】二叉树的层序遍历

[OceanApart]

https://leetcode-cn.com/problems/binary-tree-level-order-traversal/

[Brand0n-Zhang]

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrder = function (root) {
  if (!root) return [];
  let resultList = []
  let stepList = []
  stepList.push(root)
  function loop (stepList) {
    let newStepList = []
    let valList = []
    for (const item of stepList) {
      if (item.left) {
        newStepList.push(item.left)
      }
      if (item.right) {
        newStepList.push(item.right)
      }
      valList.push(item.val)
    }
    resultList.push(valList)
    if (newStepList.length > 0) {
      loop(newStepList)
    }
  }
  loop(stepList)
  return resultList
};

[OceanApart]

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrder = function(root) {
  var queue = [ root ]
  var res = []

  // 空树
  if (!root) return res

  // 队列不为空
  while (queue.length !== 0) {
    var levelResult = []
    var node
    let count = queue.length

    while (count--) {
      node = queue.shift()
      levelResult.push(node.val)

      // 左右节点放到下一层队列
      if (node.left !== null) queue.push(node.left)
      if (node.right !== null) queue.push(node.right)
    }

    // 当前层结果
    res.push(levelResult)
  }

  return res
};