Discussion About Next Greater Element

#1

This is Discussion thread about Next Greater Element

#2

The code is compiling and running but when i’m subitting the code it’s showing wrong answer while the output is right.
import java.util.*;
public class Main {

public static void main(String args[]) throws Exception {
	// Your Code Here
	Scanner s = new Scanner(System.in);
	
	int t = s.nextInt();
	while(t-- > 0){
		
		int N=s.nextInt();
		int[] nums=new int[N];
		for(int i=0;i<N;i++){
			nums[i]=s.nextInt();
		}
        
        Main obj = new Main();
        StacksUsingArrays stack = obj.new StacksUsingArrays();
		int[] ans=NextGreater(nums, stack);
		for(int i=0;i<ans.length;i++){
			System.out.println(nums[i]+","+ans[i]+" ");
		}
// 		System.out.println();
	}

}

public static int[] NextGreater(int[] nums,StacksUsingArrays stack) throws Exception {
    
  //Write your code here
		int n = nums.length;
	stack.push(nums[0]);
	int m = 0;
	int[] arr = new int[n];
	int element, next;

	for (int i = 1; i < n; i++) {

		if (!stack.isEmpty()) {
			next = nums[i];
			element = stack.pop();
			while (element < next) {
				arr[m] = next;
				m++;
				if (stack.isEmpty()) {
					break;
				}
				element = stack.pop();
			}
			if (element > next) {
				stack.push(element);
			}
			stack.push(next);

		}
	}
	while (!stack.isEmpty()) {
		stack.pop();
		arr[m] = -1;
		m++;
	}

	return arr;
}

private class StacksUsingArrays {
	private int[] data;
	private int tos;

	public static final int DEFAULT_CAPACITY = 10;

	public StacksUsingArrays() throws Exception {
		// TODO Auto-generated constructor stub
		this(DEFAULT_CAPACITY);
	}

	public StacksUsingArrays(int capacity) throws Exception {
		if (capacity <= 0) {
			System.out.println("Invalid Capacity");
		}
		this.data = new int[capacity];
		this.tos = -1;
	}

	public int size() {
		return this.tos + 1;
	}

	public boolean isEmpty() {
		if (this.size() == 0) {
			return true;
		} else {
			return false;
		}
	}

	public void push(int item) throws Exception {
		if (this.size() == this.data.length) {
			throw new Exception("Stack is Full");
		}
		this.tos++;
		this.data[this.tos] = item;
	}

	public int pop() throws Exception {
		if (this.size() == 0) {
			throw new Exception("Stack is Empty");
		}
		int retVal = this.data[this.tos];
		this.data[this.tos] = 0;
		this.tos--;
		return retVal;
	}

	public int top() throws Exception {
		if (this.size() == 0) {
			throw new Exception("Stack is Empty");
		}
		int retVal = this.data[this.tos];
		return retVal;
	}

	public void display() throws Exception {
		if (this.size() == 0) {
			throw new Exception("Stack is Empty");
		}
		for (int i = this.tos; i >= 0; i--) {
			System.out.println(this.data[i]);
		}

	}

}

}