Algorithm to find Minimum Distance Between BST (binary search tree) Nodes

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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.
Answered question
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HackerAlgo (anonymous) 0 Comments
  • Traverse the tree using tree traversal algorithm for e.g. inorder
  • Push all the traversed nodes in an array.
  • Sort the array
  • Find the minimum difference between array elements by looping through

Javascript code below:-

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var minDiffInBST = function(root) {
    var arr = [];
         inorder(root, arr);
              arr.sort((a,b)=>a-b);
    var minDiff = Number.MAX_SAFE_INTEGER;
                 var result = [];
    var map = {};
         for (var i = 0; i < arr.length; i++) {
        if (typeof map[arr[i]] === 'undefined') {
            map[arr[i]] = arr[i];
        }
                 if (i < arr.length - 1 && Math.abs(arr[i+1] - arr[i]) < minDiff) {
            minDiff = arr[i+1] - arr[i];
        }
    }
             return minDiff;
};
 var inorder = function(root, arr) {
    if (root) {
        inorder(root.left, arr);
        arr.push(root.val);
        inorder(root.right, arr);
    }
}

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