leetcode-617. 合并二叉树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        TreeNode* root = NULL;
        root =  merge(root1,root2);
        return root;
    }
    TreeNode* merge(TreeNode* root1, TreeNode* root2){
        int res = 0;
        TreeNode* root = NULL; // 创建跟节点
        if(root1==NULL&&root2==NULL)
            return NULL;
        if(root1==NULL){
            res = root2->val;
            root = new TreeNode(res);
            root->left = merge(NULL,root2->left);
            root->right = merge(NULL,root2->right);
        }

        if(root2==NULL){
            res = root1->val;
            root = new TreeNode(res);
            root->left = merge(root1->left,NULL);
            root->right = merge(root1->right,NULL);
        }

        if(root1!=NULL&&root2!=NULL){
            res = root1->val + root2->val;
            root = new TreeNode(res);
            root->left = merge(root1->left,root2->left);
            root->right = merge(root1->right,root2->right);
        }

        return root;
    }
};

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

        return root;
    }

};