[数据结构与算法]LeetCode 617. 合并二叉树

class Solution {
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        if(root1==NULL&&root2==NULL)
            return NULL;
        else if(root1==NULL)
            return root2;
        else if(root2==NULL)
            return root1;
        else if(root1&&root2)
            root1->val=root1->val+root2->val;
        if(root1->left==NULL&&root2->left)
            root1->left=new TreeNode(0);
        mergeTrees(root1->left,root2->left);
        if(root1->right==NULL&&root2->right)
            root1->right=new TreeNode(0);
        mergeTrees(root1->right,root2->right);
        return root1;
    }
};