【LeetCode热题100】【二叉树】二叉搜索树中第K小的元素

class Solution {
public:
    vector<int> nums;

    void inOrder(TreeNode *root) {
        if (root == nullptr)
            return;
        inOrder(root->left);
        nums.push_back(root->val);
        inOrder(root->right);
    }

    int kthSmallest(TreeNode *root, int k) {
        inOrder(root);
        return nums[k - 1];
    }
};