LeetCode OJ 230. Kth Smallest Element in a BST
Given a binary search tree, write a function kthSmallest
to find the kth smallest element in it.
Note:
You may assume k is always valid, 1 ≤ k ≤ BST's total elements.
Follow up:
What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?
Hint:
- Try to utilize the property of a BST.
- What if you could modify the BST node's structure?
- The optimal runtime complexity is O(height of BST).
Credits:
Special thanks to @ts for adding this problem and creating all test cases.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
private int cnt = 0;
public int kthSmallest(TreeNode root, int k) {
int result = 0;
if(root != null){
result = kthSmallest(root.left,k);
cnt++;
if(cnt == k){
return root.val;
}
result += kthSmallest(root.right,k);
}
return result;
}
}
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