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by Sumit Chourasia | Oct 09, 2020 | Category :coding | Tags : algorithm binary-tree data-structure easy leetcode tree

Minimum Distance Between BST Nodes - Tree - Easy - LeetCode

Minimum Distance Between BST Nodes - Tree - Easy - LeetCode

Given a Binary Search Tree (BST) with the root node root, return the minimum difference between the values of any two different nodes in the tree.

Example :

Input: root = [4,2,6,1,3,null,null]
Output: 1
Explanation:
Note that root is a TreeNode object, not an array.

The given tree [4,2,6,1,3,null,null] is represented by the following diagram:

          4
        /   \
      2      6
     / \    
    1   3  

while the minimum difference in this tree is 1, it occurs between node 1 and node 2, also between node 3 and node 2.
Note:

The size of the BST will be between 2 and 100.
The BST is always valid, each node's value is an integer, and each node's value is different.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    int min=int.MaxValue;
    int? prev = null;
    public int MinDiffInBST(TreeNode root) {
        Helper(root);
        return min;
    }
    
    private void Helper(TreeNode root){
        if(root==null){
            return;
        }
        
        Helper(root.left);
        if(prev!=null){
            min = Math.Min(min,root.val-(int)prev);
        }
        prev = root.val;
        Helper(root.right);
    }
}

Time Complexity: O(n)

Space Complexity: O(1)