GCJ2020-Q3: Parenting Partnering Returns

#include <iostream>
#include <vector>
#include <queue>
#include <tuple>
using namespace std;

#define tiii tuple<int, int, int>

int q, nt;

int main(){

    int s, e, in, c, j;
    bool inv;

    scanf("%d", &q);
    for(int k = 1; k <= q; ++k){
        scanf("%d", &nt);
        priority_queue<tiii, vector<tiii>, greater<tiii>> q;
        vector<char> ans(nt, '\0');
        for(int i = 0; i < nt; ++i){
            scanf("%d %d", &s, &e);
            q.push(make_tuple(s, e, i));
        }
        inv = false;
        c = 0;
        j = 0;
        while(!q.empty()){
            s = get<0>(q.top());
            e = get<1>(q.top());
            in = get<2>(q.top());
            q.pop();
            if(s < c && s < j){
                inv = true;
                break;
            } else if(s >= c){
                ans[in] = 'C';
                c = e;
            } else {
                ans[in] = 'J';
                j = e;
            }
        }
        cout << "Case #" << k << ": ";
        if(inv){
            cout << "IMPOSSIBLE\n";
        } else {
            for(auto x : ans){
                cout << x;
            }
            cout << "\n";
        }
    }

    return 0;
}