Leetcode617. 两个二叉树相加

题目描述

和leetcode226.翻转二叉树非常相似，核心还是递归。
答案：

    class Solution {
        public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
            if (root1 == null) {
                return root2;
            }

            if (root2 == null) {
                return root1;
            }

            TreeNode root = new TreeNode();
            root.val = root1.val + root2.val;
            root.left = mergeTrees(root1.left, root2.left);
            root.right = mergeTrees(root1.right, root2.right);
            return root;
        }
    }