题意:
给定二叉树,返回其节点值的级别顺序遍历。
For example:
Given binary tree{3,9,20,#,#,15,7},
3
/ \
9 20
/ \
15 7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
import java.util.*;
public class Solution {
public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
LinkedList<TreeNode> que = new LinkedList<TreeNode>();
ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
if(root==null)return res;
que.add(root);
while(!que.isEmpty()){
int size = que.size();
ArrayList<Integer> list = new ArrayList<Integer>();
for(int i=0;i<size;i++){
TreeNode cur = que.pop();
list.add(cur.val);
if(cur.left!=null){
que.add(cur.left);
}
if(cur.right!=null){
que.add(cur.right);
}
}
res.add(list);
}
return res;
}
}