Next Greater Element

#include 
     using namespace std;
     int main()
    {  

    int t;
    cin>>t;
    while(t--)
    {
    int n;
    cin>>n;
    int a[n];
    for(int i=0;i>a[i];

    stack s; 

    int ans[n]; 

    for (int i = n - 1; i >= 0; i--)  
    { 
        while (!s.empty() && s.top() <= a[i]) 
            s.pop(); 
        if (s.empty())  
            ans[i] = 0;          
        else 
            ans[i] = s.top();         

        s.push(a[i]); 
    } 

    for(int i=0;i

						 

import java.util.Stack;
class Prepbytes {

    // This function will find the next greater element for each 
    // element
    public static int[] nextGreaterElement(int arr[], int n)
    {
          Stack<Integer> st = new Stack<>();
	    int ans[] = new int[n];
	    
	    // Iterate over the given array
	    for(int i = n - 1; i>= 0; i--){
	        
	        // While stack is not empty and the current
	        // element is greater than the top of the
	        // stack, keeping removing the top of the stack
	        while(!st.isEmpty() && arr[i] >= st.peek()){
	            st.pop();
	        }
	        
	        // If the stack is empty, then it mean there is no next greater
	        // element for this element
	        if(st.isEmpty()){
	            ans[i] = -1;
	        } 
	        // Otherwise, the top of the stack is the next greater
	        // element for this element
	        else {
	            ans[i] = st.peek();
	        }
	        
	        // Push the current element to the stack
	        st.push(arr[i]);
	    }
	    return ans;

    }
    
    public static void main(String[] args) {
        int arr[] = new int[]{1, 4, 2, 17, 9, 12};
        int ans[] = nextGreaterElement(arr, arr.length);
        for(int e : ans){
            System.out.print(e+" ");
        }
    }
}

# your code goes herefor _ in range(int(input())):
    n = int(input())
    a = list(map(int,input().split()))
    s = []
    ans = [0 for i in range(n)]
    for i in range(n-1, -1, -1):
        while s and s[-1] <= a[i]:
            s.pop()
        if not s:
            ans[i] = 0
        else:
            ans[i] = s[-1]
        s.append(a[i])
    print(*ans)