siriya.cpp

/**
 * @author Lakshith Nishshanke
 * @brief 
 * @version 0.1
 * @date 2021-10-23
 * 
 * @copyright Copyright (c) 2021
 * 
 * Used a greedy approach. Sorted time frames first by their starting time,second by their endind time.
 * And then greedily checked if it is possible to reserve dates in the sorted order.
 * I don't have a mathematical proof but considering constraints solution should be approx. O(n log n). Too much for DP.
 * So should be a greedy. Hope this works
 */

#include <bits/stdc++.h>

using namespace std;

inline void io(){
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
}

void solve(){
    int n;
    cin >> n;
    vector<pair<int,int>> vec;
    for(int i=0;i<n;i++){
        int a,b;
        cin >> a >> b;
        vec.push_back({a,b});
    }
    sort(vec.begin(),vec.end());
    vector<int> ans;
    int day = vec[0].first;
    int pat = 0;
    for(int i=0;i<n;i++){
        if(vec[pat].second<day||vec[pat].first>day){
            cout << "IMPOSSIBLE\n";
            return;
        }
        ans.push_back(pat++);
        day++;
    }
    for(int x:ans)cout << x+1 << " ";
    cout << "\n";
}

signed main(){
    //comment before submision
	freopen("in", "r", stdin);
	freopen("out", "w", stdout);

	io();
	int n;
	cin >> n;
	while(n--)
		solve();
	return 0;
}