207、合并二叉树

题目描述：

注意: 合并必须从两个树的根节点开始。
肯定是递归实现
代码：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
    if(t1 == null){
			return t2;
		}
		if(t2 == null){
			return t1;
		}
		t1.val = t1.val + t2.val;
		t1.left = mergeTree(t1.left, t2.left);
		t1.right = mergeTree(t1.right, t2.right);
		return t1;
    }
	public TreeNode mergeTree(TreeNode t1, TreeNode t2){
		if(t1 == null){
			return t2;
		}
		if(t2 == null){
			return t1;
		}
		t1.val = t1.val + t2.val;
		t1.left = mergeTree(t1.left, t2.left);
		t1.right = mergeTree(t1.right, t2.right);
		return t1;
	}
}

效率还行