二叉搜索树中第K小的元素

Posted 2022-02-09 Alice_yufeng

/**
 * Definition for a binary tree node.
 * public class TreeNode 
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() 
 *     TreeNode(int val)  this.val = val; 
 *     TreeNode(int val, TreeNode left, TreeNode right) 
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     
 * 
 */
class Solution 
    int ans, k;
    public int kthSmallest(TreeNode root, int k) 
        this.k = k;
        dfs(root);
        return ans;
    

    public void dfs(TreeNode root)
        if(root == null) return;
        dfs(root.left);
        k--;
        if(k == 0)
            ans = root.val;
            return;
        
        dfs(root.right);