[Leetcode 617] Merge Two Binary Trees

Input: root1 = [1,3,2,5], root2 = [2,1,3,null,4,null,7]
Output: [3,4,5,5,4,null,7]
Input: root1 = [1], root2 = [1,2]
Output: [2,2]
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
struct TreeNode* mergeTrees(struct TreeNode* root1, struct TreeNode* root2){
if(!root1 && !root2)
return NULL;
if(!root1)
return root2;
if(!root2)
return root1;

root1->val += root2->val;

root1->left = mergeTrees(root1->left, root2->left);
root1->right = mergeTrees(root1->right, root2->right);

return root1;
}

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