Method mergeTrees

memo/treenode.cpp:24–37

class Solution {
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        if(root1 == nullptr && root2 == nullptr) {
            return nullptr;
        } else if (root1 == nullptr) {
            return root2;
        } else if (root2 == nullptr) {
            return root1;
        } else {
            TreeNode* root = new TreeNode(root1->val + root2->val);
            root->left = mergeTrees(root1->left, root2->left);
            root->right = mergeTrees(root1->right, root2->right);
            return root;
        }
    }
};