Check if a given array can represent Preorder Traversal of Binary Search Tree

// Java program for an efficient solution to check if 
// a given array can represent Preorder traversal of 
// a Binary Search Tree 
import java.util.Stack; 
  
class BinarySearchTree { 
  
    boolean canRepresentBST(int pre[], int n) { 
        // Create an empty stack 
        Stack<Integer> s = new Stack<Integer>(); 
  
        // Initialize current root as minimum possible 
        // value 
        int root = Integer.MIN_VALUE; 
  
        // Traverse given array 
        for (int i = 0; i < n; i++) { 
            // If we find a node who is on right side 
            // and smaller than root, return false 
            if (pre[i] < root) { 
                return false; 
            } 
  
            // If pre[i] is in right subtree of stack top, 
            // Keep removing items smaller than pre[i] 
            // and make the last removed item as new 
            // root. 
            while (!s.empty() && s.peek() < pre[i]) { 
                root = s.peek(); 
                s.pop(); 
            } 
  
            // At this point either stack is empty or 
            // pre[i] is smaller than root, push pre[i] 
            s.push(pre[i]); 
        } 
        return true; 
    } 
  
    public static void main(String args[]) { 
        BinarySearchTree bst = new BinarySearchTree(); 
        int[] pre1 = new int[]{40, 30, 35, 80, 100}; 
        int n = pre1.length; 
        if (bst.canRepresentBST(pre1, n) == true) { 
            System.out.println("true"); 
        } else { 
            System.out.println("false"); 
        } 
        int[] pre2 = new int[]{40, 30, 35, 20, 80, 100}; 
        int n1 = pre2.length; 
        if (bst.canRepresentBST(pre2, n) == true) { 
            System.out.println("true"); 
        } else { 
            System.out.println("false"); 
        } 
    } 
} 
  
//This code is contributed by Mayank Jaiswal