【leetcode】102. Binary Tree Level Order Traversal

/**
* 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>> result = new ArrayList<List<Integer>>();
levelOrder(root,0,result);
return result;
}
//add root
public void levelOrder(TreeNode root, int level, List<List<Integer>> result) {
if(root == null)
return;

List<Integer> temp = null;
if(result.size()<level+1){
temp = new ArrayList<Integer>();
result.add(temp);
}else{
temp = result.get(level);
}

temp.add(root.val);
levelOrder(root.left,level+1,result);
levelOrder(root.right,level+1,result);
}
}