思路:
选择其中一棵树,如果对应的两个节点都不为null,则将值相加.以此方式先遍历左边,再遍历右边.
/** * 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+=t2.val; t1.left=mergeTrees(t1.left,t2.left); t1.right=mergeTrees(t1.right,t2.right); return t1; } }