Kth Smallest Element in a BST

最新推荐文章于 2025-09-12 17:31:31 发布

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原文链接：http://www.cnblogs.com/mrpod2g/p/4648766.html

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#数据结构与算法

本文详细介绍了如何通过中序遍历来寻找给定二叉搜索树中的第k小元素，并探讨了在二叉搜索树频繁修改的情况下优化此过程的方法。

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?

/**
 * 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 n = 0;
    private TreeNode re_node;
    
    //中序遍历二叉排序树
    public void InOrderTravel(TreeNode root,int k) {
        if(root!=null) {
            InOrderTravel(root.left,k);
            n++;
            if(n==k) {
                this.re_node = root;
                return;
            }
            InOrderTravel(root.right,k);
        }
    }
    
    
    public int kthSmallest(TreeNode root, int k) {
        InOrderTravel(root,k);
        return this.re_node.val;
    }
}