102

题目

var levelOrder = function(root) {
  if(!root)return [];
  let arr = [root];
  let ans = [[root.val]];
  while(arr.length!==0){
    const len = arr.length;
    const temp = [];
    for(let i=0;i<len;i++){
      const shift = arr.shift();
      if(shift.left){
        arr.push(shift.left);
        temp.push(shift.left.val);
      }
      if(shift.right){
        arr.push(shift.right);
        temp.push(shift.right.val);
      }
    }
    if(temp.length!==0)ans.push(temp);
  }
  return ans;
};