合并二叉树的递归算法

TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        // write code here
        TreeNode * node = new TreeNode(0);
        if(t1 == nullptr && t2== nullptr)
        {
            node = nullptr;
        }
        else if(t1 == nullptr)
        {
            node = t2;
        }
        else if(t2 == nullptr)
        {
            node = t1;
        }
        else
        {
            node->val = t1->val + t2->val;
            node->left = mergeTrees(t1->left, t2->left);
            node->right = mergeTrees(t1->right, t2->right);
        }

        return node;
    }