Binary Tree Level Order Traversal
给一个二叉树, 层序扫描. 这个最常见的扫描方法.
/**
* 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) {
ArrayList<List<Integer>> res = new ArrayList<List<Integer>>();
if(root == null)
return res;
Queue<TreeNode> queue = new LinkedList<TreeNode>();
queue.offer(root);
while(!queue.isEmpty()){
List<Integer> tmp = new ArrayList<Integer>();
int size = queue.size();
for(int i = 0 ; i < size; i++) {
TreeNode node = queue.poll();
tmp.add(node.val);
if(node.left != null)
queue.offer(node.left);
if(node.right != null)
queue.offer(node.right);
}
res.add(tmp);
}
return res;
}
}