LintCode 69---二叉树的层次遍历

/*** Definition of TreeNode:* public class TreeNode {*     public int val;*     public TreeNode left, right;*     public TreeNode(int val) {*         this.val = val;*         this.left = this.right = null;*     }* }*/public class Solution {/*** 给出一棵二叉树，返回其节点值的层次遍历（逐层从左往右）* @param root: A Tree* @return: Level order a list of lists of integer*/public List<List<Integer>> levelOrder(TreeNode root) {List<List<Integer>> result = new ArrayList<>();//判断根节点是否为空if (root == null){return result;}//定义一个队列,并添加根节点Queue<TreeNode> queue = new LinkedList<>();queue.add(root);TreeNode node = null;while (!queue.isEmpty()){int size = queue.size();List<Integer> level = new ArrayList<>();for (int i = 0; i < size; i++) {node = queue.poll();level.add(node.val);if(node.left != null){queue.add(node.left);}if(node.right != null){queue.add(node.right);}}result.add(level);}return result;}
}