617.merge-two-binary-trees.123866974.ac.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if (!t1 && !t2) {
            return nullptr;
        }
        TreeNode* root = new TreeNode((t2 ? (t2->val) : 0) + (t1 ? (t1->val) : 0));
        root->left = mergeTrees(t1 ? t1->left : nullptr, t2 ? t2->left : nullptr);
        root->right = mergeTrees(t1 ? t1->right : nullptr, t2 ? t2->right : nullptr);
        return root;
    }
};