[sword finger offer] interview question 54: the k-largest node of the binary search tree

Method 1 ： In the sequence traversal + Index count return

Because the binary search tree given by the topic
Therefore, you can traverse from large to small through the medium order traversal
But you need to traverse the right subtree first and then the left subtree

/** * 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:
    int index = 0;
    int k_value = 0;
    int kthLargest(TreeNode* root, int k) {
    

        preOrder(root, k);
        return k_value;
        
    }
    void preOrder(TreeNode* root,int k)
    {
    
        if( root == nullptr )
            return;
        preOrder(root->right,k);
        index++;
        if(index == k)
        {
    
            k_value = root->val;
            return;
        }
        preOrder(root->left,k);
    }
    
};