Can someone explain this to me?

[SuperJeRoT]

Hi people, here's the deal. I have a seminar paper to do, and I have done it but the only thing left to do is to explain the solution (I found it online to be honest) to my profesor. I tryed to explain it today but that ended no so well because I'm not 100% sure what the code does so I explaind as much as I could but that was not enogh so the prof. told me to return tomorow and explain it to her again since I was a bit angry and could not concentrate to my fullest.

 

So I ask you nicely if you can explain this code to my, what it does and how can I explain it to her?

 

I've done it in C since it must be written in C, but I have a solution in C++. It is the same, just that C++ has sort() function and in C I put selection sort, and I need a structure in C to replace pair in C++, other parts are totaly the same.

 

Here's the task:

teleporters.pdf

 

Here's the textual solution I found, but I think that the code doesn't folow this solution in particular, I coul'd be wrong though.

iarsc org.pdf

I also have this solution (page 37)

IOI2008Booklet1.0.pdf

 

 

I understand the first half of the code

And finaly here is the code I've got:

#include <algorithm>#include <iostream>#include <cassert>#include <cstdio>#include <cstring>#define NMAX 2000010using namespace std;int lookup[NMAX];pair<int,int> tel[NMAX];int N,M;char visited[NMAX];int compute_len(int st){	int i,len;	i = st;	len = 0;	while(!visited[i]){		visited[i] = 1;		if(i >= N-1) break;		i = lookup[tel[i+1].second];		++len;	}	return len;}int path;int cyc[NMAX];int C;int main(){	int i;	scanf("%d%d",&N,&M);	tel[0] = make_pair(0,-1);	for(i = 1; i <= N; ++i){		scanf("%d%d",&tel[i].first,&tel[i].second);		tel[N+i] = make_pair(tel[i].second,tel[i].first);	}	N*=2;	++N;	sort(tel,tel+N);	for(i = 0; i < N; ++i){		lookup[tel[i].first] = i;//what is lookup and what do we do with it?	}	path = compute_len(0);	for(i = 0; i < N; ++i){		if(visited[i]) continue;		cyc[C++] = compute_len(i);//what is this cyc array do, how do I explain it?	}	sort(cyc,cyc+C);	while(M-- && C){		path += cyc[--C]+2;//here is cyc again, why do we just add numbers to current path, what is the meaning of 2 here?	}//and the while part, I don't understand because I don't get those things before probably	++M;	while(M--){		if(C){			path += cyc[--C]+2;			continue;		}		path++;		cyc[C++] = 1;	}	printf("%d\n",path);	return 0;}

So if you guys can help me that would be awesome so I can earn some points and pass this damn exam finaly!

[IMPERIUS]

like if you don't know what all this even means (I want to get into programming tho)

[-TesseracT-]

like if you don't know what all this even means (I want to get into programming tho)

Like if you think this post is useless.

[lutewan]

like if you don't know what all this even means (I want to get into programming tho)

this isnt facebook

[SuperJeRoT]

I know C, I understand it since I'm learning it in coledge. But this is not my code so I don't quite know the details of what the person wanted to do with some parts of the code.

[Guest]

Its hard to read someone's code. Its best to write it by yourself. 

I want to help but task is too long that I dont have time to read it whole.

Try to write it from scratch alone and than ask for specific things. 
Pozdrav!

[SuperJeRoT]

Its hard to read someone's code. Its best to write it by yourself. 

I want to help but task is too long that I dont have time to read it whole.

Try to write it from scratch alone and than ask for specific things. 

Pozdrav!

Pozdrav brate moj!  :lol:

I've done that, I've marked the specific things I don't understand in the code. The start of the code is just reading from standard input and making a array. The function returns how many teleports I've passed going trough the Egypt.

 

In the text of the task is a lot of nonsence, the important bit is the EXAMPLE. 

Also the text solutions are not important, I just put them there so if anybody needs them then there they are 

[Guest]

Pozdrav brate moj!  :lol:

I've done that, I've marked the specific things I don't understand in the code. The start of the code is just reading from standard input and making a array. The function returns how many teleports I've passed going trough the Egypt.

 

In the text of the task is a lot of nonsence, the important bit is the EXAMPLE. 

Also the text solutions are not important, I just put them there so if anybody needs them then there they are 

As I said I must read whole task to know how how it should work and I cant do that

I read in your profile that you are going to be programmer? If you want to become programmer you should try to write it by yourself