maxcian der TechBlog

 這題有趣的應該是了解怎麼格式化輸出一棵tree去看答案對不對

TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) 
{
    if (!t1 && !t2) return NULL; // no need, bacause if t1 and t2 are NULL, return t2 as same as return NULL
    if (!t1) return t2;
    if (!t2) return t1;
    TreeNode* ret = new TreeNode(t1->val + t2->val);
    ret->left = mergeTrees(t1->left, t2->left);
    ret->right = mergeTrees(t1->right, t2->right);
    return ret;
}