Minimum Distance Between BST Nodes


#1

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:

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

#2

Since it is a BST, an inorder traversal gives us a sorted ascending order of values. So we keep track of the diff between the last value and the current value in the min and return it.

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func minDiffInBST(root *TreeNode) int {
   
    prev := math.MinInt32
    min := math.MaxInt32
    helper(root, &prev, &min)
    return min
}

func helper(root *TreeNode, prev, min *int){
    if(root==nil){return}
    helper(root.Left, prev, min)
    if(*min > root.Val - *prev){
        *min = root.Val - *prev
    }
   *prev = root.Val
   
    helper(root.Right, prev, min)
}