【二叉树 - 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) {
        if(root1 && root2){
            root1->val += root2->val;
            // 直接在 root1 上合并，所以这里递归的节点都是root1
            root1->left = mergeTrees(root1->left,root2->left);
            root1->right = mergeTrees(root1->right,root2->right);
        }
        return root1 ? root1 : root2;
    }
};