530. Minimum Absolute Difference in BST #

Problem #

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.
• This question is the same as 783:  https://leetcode.com/problems/minimum-distance-between-bst-nodes/

Problem Summary #

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

Solution Ideas #

• Since it is a BST, use its ordered property: the result of an inorder traversal is sorted. During the inorder traversal, dynamically maintain the difference between the previous and current nodes to find the minimum difference.
• This problem is exactly the same as Problem 783.

Code #

package leetcode

import (
	"math"

	"github.com/halfrost/leetcode-go/structures"
)

// TreeNode define
type TreeNode = structures.TreeNode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

func getMinimumDifference(root *TreeNode) int {
	res, nodes := math.MaxInt16, -1
	dfsBST(root, &res, &nodes)
	return res
}

func dfsBST(root *TreeNode, res, pre *int) {
	if root == nil {
		return
	}
	dfsBST(root.Left, res, pre)
	if *pre != -1 {
		*res = min(*res, abs(root.Val-*pre))
	}
	*pre = root.Val
	dfsBST(root.Right, res, pre)
}

func min(a, b int) int {
	if a > b {
		return b
	}
	return a
}

func abs(a int) int {
	if a > 0 {
		return a
	}
	return -a
}