https://leetcode.com/problems/validate-binary-search-tree

validate-binary-search-tree.go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isValidBST(root *TreeNode) bool {
    return checkIsValid(root, -1 << 32, (1 << 32) - 1)
}

func checkIsValid(root *TreeNode, from, to int) bool {
    if root == nil {
        return true
    }
    
    if root.Val <= from || root.Val >= to {
        return false
    }
    
    return checkIsValid(root.Left, from, root.Val) && checkIsValid(root.Right, root.Val, to)
}