530 Minimum Absolute Difference in BST¶

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

Example:

Input:

   1
    \
     3
    /
   2

Output:
1

Explanation:
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.

Idea:

Sorting via inorder traversal gives us sorted values, compare current one with previous one to reduce space complexity from O(n) to O(h).

alt

Solution:¶

// Runtime: 16 ms
class Solution {
    public int getMinimumDifference(TreeNode root) {
        prev_ = null;
        min_diff_ = Integer.MAX_VALUE;
        inorder(root);
        return min_diff_;
    }

    private void inorder(TreeNode root) {
        if (root == null) return;
        inorder(root.left);
        if (prev_ != null) min_diff_ = Math.min(min_diff_, root.val - prev_);
        prev_ = root.val;
        inorder(root.right);
    }

    private Integer prev_;
    private int min_diff_;