Leetcode 270: Closest Binary Search Tree Value

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

Note:

• Given target value is a floating point.
• You are guaranteed to have only one unique value in the BST that is closest to the target.

 

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int ClosestValue(TreeNode root, double target) {
        TreeNode candidate = null;
        DFS(root, target, ref candidate);
        return candidate.val;
    }
    
    private void DFS(TreeNode node, double target, ref TreeNode candidate)
    {
        if (node == null) return;
        
        if (candidate == null || (Math.Abs((double)node.val - target) < Math.Abs((double)candidate.val - target))) 
        {
            candidate = node;
        }
        
        if ((double)node.val > target)
        {
            DFS(node.left, target, ref candidate);
        }
        else
        {
            DFS(node.right, target, ref candidate);
        }
    }
}