Leetcode 102 Binary Tree level Order Traversal-----java

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,null,null,15,7] ,

    3   /   9    /   7

Return its level order traversal as:

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

It's easy to output every row of a tree.

/*** Definition for a binary tree node. * public class TreeNode {* int val; * TreeNode left; * TreeNode RI Ght * TreeNode (int x) {val = x;} }*/ Public classSolution { PublicList<list<integer>>Levelorder (TreeNode root) {List List=NewArraylist<list<integer>>(); if(Root = =NULL)            returnlist; Queue<TreeNode> queue =NewLinkedlist<treenode>();        Queue.add (root);  while( !Queue.isempty ()) {List ans=NewArraylist<integer>(); intSize =queue.size ();  for(inti = 0;i<size;i++) {TreeNode node=Queue.poll (); if(node = =NULL)                    Continue;                Ans.add (Node.val);                Queue.add (Node.left);            Queue.add (Node.right); }            if(Ans.size ()! = 0) list.add (ans); }                        returnlist; }}

Leetcode 102 Binary Tree level Order Traversal-----java