package nextgreaterelement;

import java.util.Arrays;
import java.util.Stack;

public class app {
    public static void main(String[] args) {
        int arr[] = {1, 2, 4, 8, 6, 10};
		
        
        
        System.out.println(Arrays.toString(nextGreater(arr)));
    }

    static int[] nextGreater(int arr[]) {
        Stack<Integer> stack = new Stack<>();

        stack.push(arr[arr.length-1]);

        int a[] = new int[arr.length];
      
        
        a[arr.length-1] = -1;

        for (int i = arr.length-2; i >= 0; i--) {
            while (!stack.isEmpty() &&              
                    stack.peek() <= arr[i]) {

                stack.pop();                        
            }

            if (stack.isEmpty())
                a[i] = -1;                           
            else
                a[i] = stack.peek();

            stack.push(arr[i]);
        }

        return a;
    }
}

//Output:
//        2 4 8 10 10 -1