leetcode 1305. 两棵二叉搜索树中的所有元素

/**
 * 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:
    void dfs(TreeNode* node, vector<int>& ans) {
        if (!node) {
            return;
        }
        ans.push_back(node->val);
        dfs(node->left, ans);
        dfs(node->right, ans);
    }

    vector<int> getAllElements(TreeNode* root1, TreeNode* root2) {
        vector<int> ans;
        dfs(root1, ans);
        dfs(root2, ans);
        sort(ans.begin(), ans.end());
        return ans;
    }
};