230. Kth Smallest Element in a BST (Medium)

https://leetcode.com/problems/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.

Example 1:

Input: root = [3,1,4,null,2], k = 1
   3
  / \
 1   4
  \
   2
Output: 1

Example 2:

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

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?

Hints

Solutions

https://www.programcreek.com/2014/07/leetcode-kth-smallest-element-in-a-bst-java/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int kthSmallest(TreeNode root, int k) {
        Stack<TreeNode> stack = new Stack<TreeNode>();

        TreeNode p = root;
        int result = 0;

        while(!stack.isEmpty() || p!=null){
            if(p!=null){
                stack.push(p);
                p = p.left;
            }else{
                TreeNode t = stack.pop();
                k--;
                if(k==0)
                    result = t.val;
                p = t.right;
            }
        }

        return result;
    }
}
Copyright © iovi.com 2017 all right reserved,powered by GitbookLast Modification: 2019-04-09 12:09:36

results matching ""

    No results matching ""