力扣617 合併二叉樹 遞歸

/**
 * 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==nullptr&&t2==nullptr) return nullptr;
        if(t1==nullptr&&t2!=nullptr) return t2;
        if(t1!=nullptr&&t2==nullptr) return t1;
        TreeNode* newtree=new TreeNode(t1->val+t2->val);
        newtree->left=mergeTrees(t1->left,t2->left);
        newtree->right=mergeTrees(t1->right,t2->right);
        return newtree;

    }
};