Node k-th largest face questions 54. leetcode-- binary search tree

K-th largest face questions node 54. The binary search tree
given a binary search tree, please find out the k-th largest nodes.

Example:

Input: root = [5,3,6,2,4, null, null, 1], k = 3 Output: 4
Input: root = [3,1,4, null, 2], k = 1 Output: 4

``````      5
/ \
3   6
/ \
2   4
/
1

3
/ \
1   4
\
2
``````

limit:

1 ≤ k ≤ number of the binary search tree element

A thought: non-recursive

``````/**
* 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 kthLargest(TreeNode* root, int k) {
stack<TreeNode*> stack;
//vector<int> nums;
int n = 0;
TreeNode* p = root;
while (p || !stack.empty()){
while (p){
stack.push(p);
p = p->right;
}
p = stack.top();
stack.pop();
//nums.push_back(p->val);
n++;
if (n == k){
return p->val;
}
p = p->left;
}
return 0;
}
};
/*20ms,26.6MB*/
``````

Ideas II: recursive

``````class Solution {
private:
int ans = 0;
int n = 0;
public:
int kthLargest(TreeNode* root, int k) {
InOrderTraverse(root, k);
return ans;
}
void InOrderTraverse(TreeNode* root, int k){
if (root == NULL){
return;
}
InOrderTraverse(root->right, k);
n++;
if (n == k){
ans = root->val;
return;
}
InOrderTraverse(root->left, k);
return;
}
};
/*16ms,26.8MB*/
``````
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