maximum_difference_between_node_and_ancestor.go

package main

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

func maxAncestorDiff(root *TreeNode) int {
	res := 0
	if root == nil {
		return res
	}
	dfs(root, root.Val, root.Val, &res)

	return res
}

func dfs(root *TreeNode, minimum, maximum int, res *int) {
	if root == nil {
		return
	}
	minimum, maximum = min(root.Val, minimum), max(root.Val, maximum)
	*res = max(*res, maximum-minimum)

	dfs(root.Left, minimum, maximum, res)
	dfs(root.Right, minimum, maximum, res)
}

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

	return b
}

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

	return b
}