Rainbow Sort

#include <bits/stdc++.h>
using namespace std;



void solve() {
    int n; cin >> n;

    vector<int> v(1e5 + 3, 0), res ;
    bool ok = 1;
    for(int i=1; i<=n; ++i) {
        int x; cin >> x;
        if(v[x] == 0) res.push_back(x), v[x] = i;
        else {
            if(v[x] != i-1) ok = 0;
            else v[x] = i;
        }
    }

    if(ok) for(auto x : res) cout << x << ' ';
    else cout << "IMPOSSIBLE";
    cout << '\n';
}

int main() {
    int q; cin >> q;
    for(int i=1; i<=q; ++i) {
        cout << "Case #" << i << ": ";
        solve();
    }
    return 0;
}