# IPCTRAIN - Editorial

Primary Tester: Misha Chorniy
Editorialist: Hussain Kara Fallah

Easy

Greedy,Heap

### PROBLEM:

You have an upcoming camp. There are N trainers. The camp runs for D days.Each day,there can be at most one lecture. The ith trainer arrives on day Di and then stays till the end of the camp. He also wants to teach exactly Ti lectures. For each lecture that a trainer was not able to teach,his sadness level will be increased by Si.
You are the main organizer of the contest. You want to find minimum total sadness of the trainers.

### EXPLANATION:

Let’s assign our trainers starting from the first day of the camp. At each day adding arriving trainers to our set of trainers.

Each day should be assigned to only one trainer, it’s obvious that we should assign the trainer with maximum sadness to this lecture, so our set (container) should be a heap sorting trainers by their sadness value. In fact we should know also the number of days each lecturer wants to serve in, so we take the lecturer with maximum sadness from our heap and decrease his demand by 1. In case he still has lectures he would like to do, we keep him in the heap, otherwise we just pop him out.

After finishing all days, some teachers may have some remaining lectures they wanted to teach but we couldn’t find such days for them. Let’s denote the number of lectures the ith trainer couldn’t teach by remi So our answer would be :

answer = \sum_{i=1}^{i=N} rem_i * S_i

### AUTHOR’S AND TESTER’S SOLUTIONS:

AUTHOR’s solution: Will be found here
TESTER’s solution: Will be found here
EDITORIALIST’s solution: Will be found here

4 Likes

solutions are not available yet!!

This question literally screamed “PRIORITY QUEUE” in my ears. One of the good questions which can be solved with knowledge of proper data type!!

Honestly, i saw priority queue code for first time in “Cooking Schedule” editorial (one of the answers told that “it can also be solved using priority queue”) and it made life so simple for me here.

12 Likes

I have used Segment Trees

2 Likes

community - need help to understand what is missing https://www.codechef.com/viewsolution/14559868. only 40 pts

Can anyone explain where I went wrong? 40 pts.

https://www.codechef.com/viewsolution/14561290

Hi!

can anyone explain why i m getting WA for last 2 subtask.
https://www.codechef.com/viewsolution/14601668

@lord_ozb:
You have used a double loop here which caused the time to exceed the limit.

                for(int i = 0; i < d; i++){
int x = -1;
int max = Integer.MIN_VALUE;
for(int j = 0; j <= i; j++){
if(queue[j].size() != 0){
Trainer temp = queue[j].peek();
x = j;
1 Like

inside practice, contest link is given while in contest, practice session link is given, plz interchange those at top of editorial

I solved it using set

https://www.codechef.com/viewsolution/14578928

If I solve the above question using heaps as stated, then on popping out the trainer which doesn’t have any lecture remaining and at the very same time maintaining the sort would require the complexity O(n).
On the other hand if we just extract him from the heap and heapify using time complexity O(lg n) would disturb the sort. How do i proceed?

Links to practice and competition are backwards.

I guess I had gone mad because I couldn’t think of such a simple solution. So I did this using segment trees.
O(n*log(n)*log(n))
https://www.codechef.com/viewsolution/14497188

Can anyone help me? Author solution I seem that complexity O(N*T).Here N=100000 and T=100000 according to Constraints.How it’s passed all test case.May be something i miss.Thanks in advance.

1 Like

Links for all tutorials of July long challange for practice and contest seem to be swapped. Please consider correcting them .

Could someone please tell me why I’m a getting a TLE in my solution. I’ve used priority queue.

https://www.codechef.com/viewsolution/16505429

please explain how to implement priority queue here?? i am not able to understand plz tell @vijju123