二叉树的层次遍历

{3,9,20,#,#,15,7}

3
/ \
9  20
/  \
15   7

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

import java.util.*;
import java.util.Queue;
/**
* Created by jason on 2016/3/8.
*/
class Solution72 {
public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
Queue<TreeNode> queue = new LinkedList<TreeNode>();
if (root == null) return result;
queue.offer(root);
while (!queue.isEmpty()) {
ArrayList<Integer> val = new ArrayList<Integer>();
int size = queue.size();
for (int i=0; i<size; i++) {
TreeNode head = queue.poll();
val.add(head.val);
if (head.left != null) {
queue.offer(head.left);
}
if (head.right != null) {
queue.offer(head.right);
}
}
result.add(val);
}
return result;
}
}