(617)Merge Two Binary Trees

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