题解 | #合并二叉树#

using System;
using System.Collections.Generic;

/*
public class TreeNode
{
	public int val;
	public TreeNode left;
	public TreeNode right;

	public TreeNode (int x)
	{
		val = x;
	}
}
*/

class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param t1 TreeNode类 
     * @param t2 TreeNode类 
     * @return TreeNode类
     */
    public TreeNode mergeTrees (TreeNode t1, TreeNode t2) {
        if(t1 == null) return t2;
        if(t2 == null) return t1;
        MergeTrees2(t1, t2);
        return t1;
    }
    public void MergeTrees2(TreeNode root1, TreeNode root2){
        root1.val = root1.val + root2.val;
        if(root1.left == null || root2.left == null) {
            if(root1.left == null) root1.left = root2.left;
        }
        else MergeTrees2(root1.left, root2.left);

        if(root1.right == null || root2.right == null) {
            if(root1.right == null) root1.right = root2.right;
        }
        else MergeTrees2(root1.right, root2.right);
        return;
    }
}