2020-07-25 102. Binary Tree Leve

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

/**

• 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 res = [];
  let queue = [root];
  while(queue.length>0) {
  let stack = [];
  for(let i=queue.length; i>0; i--){
  let cur = queue.shift();
  stack.push(cur.val);
  if(cur.left) {
  queue.push(cur.left);
  }
  if(cur.right) {
  queue.push(cur.right);
  }
  }
  res.push(stack);
  }
  return res;
  };