Next Greater Element

//{ Driver Code Starts
#include<bits/stdc++.h>
using namespace std;


// } Driver Code Ends
class Solution
{
    public:
    //Function to find the next greater element for each element of the array.
    vector<long long> nextLargerElement(vector<long long> arr, int n){
        // Your code here
        stack<long long> s;
        vector<long long> ans(n,0);

        for(int i=0;i<arr.size();i++)
        {

            if(s.empty())
            {
                s.push(i);
                continue;
            }
            while(!s.empty() && arr[s.top()]<arr[i])
            {
                ans[s.top()]=arr[i];
                s.pop();
            }
            s.push(i);

        }
        while(!s.empty())
        {
            ans[s.top()]=-1;
            s.pop();
        }
        return ans;
    }
};

//{ Driver Code Starts.

int main()
{
    int t;
    cin>>t;
    while(t--)
    {

        int n;
        cin>>n;
        vector<long long> arr(n);
        for(int i=0;i<n;i++)
            cin>>arr[i];

        Solution obj;
        vector <long long> res = obj.nextLargerElement(arr, n);
        for (long long i : res) cout << i << " ";
        cout<<endl;
    }
    return 0;
}
// } Driver Code Ends