# Find the Minimum Absolute Difference in BST using Java

## The question

Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.

**Example:**

Input:1 \ 3 / 2Output:1Explanation:The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).

**Note:**

- There are at least two nodes in this BST.

## The solution

We will start with a stub to build out:

```
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public int getMinimumDifference(TreeNode root) {
}
}
```

Of this, the meat really comes in with the `getMinimumDifference`

method.

So let’s use Depth First Search (`DFS`

) to solve this problem.

```
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
// Store our list of points
public List<Integer> list = new ArrayList<>();
// Store the max differences
public int dif = Integer.MAX_VALUE;
// Our DFS method
public void dfs(TreeNode root) {
// return if not exists
if(root == null) return;
// recurse left
dfs(root.left);
// add the current node
list.add(root.val);
// recurse right
dfs(root.right);
}
// Main entry point, takes in the TreeNode's root
public int getMinimumDifference(TreeNode root) {
// do our DFS on the tree
dfs(root);
// loop through our `list`
for(int i=1;i<list.size();i++) {
// primary conditional
if(Math.abs(list.get(i) - list.get(i - 1)) < dif)
// set the difference int
dif = Math.abs(list.get(i) - list.get(i - 1));
}
// Return the difference as an integer
return dif;
}
}
```