102. Binary Tree Level Order Traversal （二叉树层次遍历）

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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  20    /  \   15   7

return its level order traversal as:

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

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List<List<Integer>> levelOrder(TreeNode root) {        List<List<Integer>> list = new LinkedList<List<Integer>>();        if(root==null)        return list;        List<Integer> intList = new LinkedList<Integer>();        Queue<TreeNode> queue = new LinkedList<TreeNode>();        TreeNode t = null;        queue.offer(root);        int curCount=0,curNum=1,nextCount=1;        while(!queue.isEmpty()){        t=queue.poll();        intList.add(t.val);        if(t.left!=null){        queue.offer(t.left);        nextCount++;        }if(t.right!=null){        queue.offer(t.right);        nextCount++;        }        if(++curCount==curNum){        list.add(intList);        intList=new LinkedList<Integer>();        curNum=nextCount;        }        }return list;    }}

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