[LeetCode][JavaScript]Binary Tree Level Order Traversal

Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3
   / \
  9  20
    /  \
   15   7

 

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

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

 

 

 

 

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按层遍历树，用一个队列记录当前层的节点，递归访问每一层。

 

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

    function traversal(){
        var top, len = queue.length, subRes = [];
        while(len--){
            top = queue.shift();
            if(top !== null && top.val !== undefined){
                subRes.push(top.val);
                queue.push(top.left);
                queue.push(top.right);
            }
        }
        if(subRes.length > 0){
            res.push(subRes);
        }
        if(queue.length > 0){
            traversal();
        }
    }
};