Nextgreater.java

import java.util.*;
public class Nextgreater {

    public static void nextGreater(int arr[], int arr1[]){
        Stack <Integer> s = new Stack<>();

        for(int i = arr.length-1; i>=0 ;i--){
            //while loop
            while(!s.isEmpty() && arr[s.peek()]<= arr[i]){
                s.pop();
            }
            //isempty check
            if(s.isEmpty()){
                arr1[i] = -1;
            }
            else{
                arr1[i] = arr[s.peek()];
            }
            //push into the stack
            s.push(i);
        }
    }
    public static void main(String args[]){
        int arr[] = {1,2,3,4,3};
        int nGreater[] = new int[arr.length];
        nextGreater(arr, nGreater);

        for(int i = 0;i<nGreater.length; i++){
            System.out.print(nGreater[i] + " ");
        }
    }
}