/*** 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==NULL&&root2==NULL)//两个二叉树都是空return NULL;if(root2!=NULL&&root1==NULL)return root2;if(root1!=NULL&&root2==NULL)return root1;root1->val=root1->val+root2->val;root1->left=mergeTrees(root1->left,root2->left);root1->right=mergeTrees(root1->right,root2->right);return root1;
}