validate_bst.go

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

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isValidBST(root *TreeNode) bool {
    if root == nil {
        return true
    }
    
    if root.Left != nil && root.Val <= max(root.Left) {
        return false
    }
    
    if root.Right != nil && root.Val >= min(root.Right) {
        return false
    }
    
    return isValidBST(root.Left) && isValidBST(root.Right)
}

func min(root *TreeNode) int {
    if root.Left == nil {
        return root.Val
    }
    
    return min(root.Left)
}

func max(root *TreeNode) int {
    if root.Right == nil {
        return root.Val
    }
    
    return max(root.Right)
}