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Program.cs
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Program.cs
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using System;
using System.Collections.Generic;
namespace ValidateBinarySearchTree
{
public class TreeNode
{
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null)
{
this.val = val;
this.left = left;
this.right = right;
}
}
class Program
{
static void Main(string[] args)
{
var a = new TreeNode(1);
var b = new TreeNode(1);
a.left = b;
Console.WriteLine(IsValidBST_Recursion(a));
}
static bool IsValidBST_Recursion(TreeNode root, long min = long.MinValue, long max = long.MaxValue)
{
if (root == null) return true;
if (root.val <= min || root.val >= max) return false;
return IsValidBST_Recursion(root.left, min, root.val) && IsValidBST_Recursion(root.right, root.val, max);
}
public bool IsValidBST_Traversal(TreeNode root)
{
var list = new List<int>();
DFS_Traversal(root, list);
for (int i = 1; i < list.Count; i++)
if (list[i] <= list[i - 1])
return false;
return true;
}
private void DFS_Traversal(TreeNode node, List<int> list)
{
if(node == null) return;
DFS_Traversal(node.left, list);
list.Add(node.val);
DFS_Traversal(node.right, list);
}
}
}