【LeetCode热题100（41/100）】二叉树的层序遍历

题目地址：链接

思路： 使用队列完成层序遍历（广度优先搜索）

/**
 * 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) {
    let ans = [];
    let pians = [];
    let q = [root];
    let nq = [];
    while(q.length) {
        let node = q.shift();
        if(!node) continue;
        pians.push(node.val);
        if(node.left) nq.push(node.left);
        if(node.right)nq.push(node.right);
        if(!q.length) {
            q = nq;
            nq = [];
            ans.push(pians);
            pians = [];
        }
    }
    return ans;
};