Grokking Data Structures & Algorithms for Coding Interviews
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Solution: Minimum Difference Between BST Nodes

Problem Statement

Given a Binary Search Tree (BST), you are required to find the smallest difference between the values of any two different nodes.

In a BST, the nodes are arranged so that the value of every node on the left is less than the root, and the value of every node on the right is greater than the root. All values are distinct, which matters here: the question asks for the smallest difference between two different nodes, and duplicates would make that difference 0.

Example

Example 1:

  • Input:
    4
   / \
  2   6
 / \
1   3
  • Expected Output: 1

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Anand Nageshwar Kumar

Anand Nageshwar Kumar

· 2 years ago

public class Solution {

    int result = Int32.MaxValue;
    int? prev =  null;
    public int GetMinimumDifference(TreeNode root) {
        DFS(root);
        return result;
    }

    private void DFS(TreeNode root)
    {
        if(root == null)
        return;

        DFS(root.left);
        if(prev.HasValue)
        result = Math.Min(result, root.val - prev.Value);
        prev = root.val;
        DFS(root.right);
    }
}
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H

Hamidou Diallo

· 2 years ago

class Solution:
    def __init__(self):
        self.min_diff = float('inf')
        self.prev = None


    def minDiffInBST(self, root):
        if not root: 
            return self.min_diff

        self.minDiffInBST(root.left)

        if self.prev:
            node_diff = abs(root.val - self.prev.val)
            self.min_diff = min(self.min_diff, node_diff)
        
        self.prev = root
        
        self.minDiffInBST(root.right)

        return self.min_diff
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Elena Feoktistova

Elena Feoktistova

· 3 years ago

public class Solution {
    public int minDiffInBST(TreeNode root) {
        int minDiff = Integer.MAX_VALUE;
        TreeNode prev = null;
        
        Stack<TreeNode> stack = new Stack<>();
        TreeNode curr = root;

        while (curr != null || !stack.isEmpty()) {
            while (curr != null) {
                stack.push(curr);
                curr = curr.left;
            }

            curr = stack.pop();

            if (prev != null) {
                minDiff = Math.min(curr.val - prev.val, minDiff);
            }
            
            prev = curr;
            
            curr = curr.right;
        }

        return minDiff;
    }
}
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