06

#include <iostream>
#include <vector>

using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

vector<int> vec;

void transfer(TreeNode* root) {
    if (root == NULL) return;
    transfer(root->left);
    vec.push_back(root->val);
    transfer(root->right);
}

int main() {
    TreeNode* root = new TreeNode(10);
    root->left = new TreeNode(5);
    root->right = new TreeNode(15);
    root->left->left = new TreeNode(3);
    root->left->right = new TreeNode(7);
    root->right->left = new TreeNode(12);
    root->right->right = new TreeNode(18);

    transfer(root);

    int k;
    cin>>k;
    for(int i=vec.size()-1;i>=0;i--)
    {
        if(vec[i]>=k)
        {
            cout<<vec[i]<<" ";
        }

    }



    return 0;
}

10

#include <iostream>

using namespace std;

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    int count;  // 记录以该节点为根的子树的节点数
    TreeNode(int x) : val(x), left(nullptr), right(nullptr), count(1) {}
};
    // 统计以node为根结点的子树的结点数
    int countNodeNum(TreeNode* node) {
        if (node == NULL) {
            return 0;
        }
        node->count = 1 + countNodeNum(node->left) + countNodeNum(node->right);
        return node->count;
    }

    // 查找第k小的元素
    int findKthSmallest(TreeNode* node, int k) {
        while (node != nullptr) {
            int leftCount = (node->left ) ? node->left->count : 0;
            if (leftCount < k - 1) {
                node = node->right;
                k -= leftCount + 1;
            } else if (leftCount == k - 1) {
                break;
            } else {
                node = node->left;
            }
        }
        return node->val;
    }
    int kthSmallest(TreeNode* root, int k) {
        countNodeNum(root);
        return findKthSmallest(root, k);
    }
  int main() {
    // 创建测试用例
    TreeNode* root = new TreeNode(5);
    root->left = new TreeNode(3);
    root->right = new TreeNode(7);
    root->left->left = new TreeNode(2);
    root->left->right = new TreeNode(4);
    root->right->left = new TreeNode(6);
    root->right->right = new TreeNode(8);
    root->left->left->left = new TreeNode(1);
    root->left->right->right = new TreeNode(4);

    cout<<kthSmallest(root,3);
    return 0;
}