runtime error sigsegv in pcycle problem

general
1

can anyone tell what is wrong in my code…
https://www.codechef.com/viewsolution/8710955

2

plzz tell my miistake in this solution

3

Try declaring b array globally outside the main function.

There seems to be some problem with your logic here too,
Refer to line 20-21
a[c]=-1;
c=a[c];

Value of c becomes negative i.e -1

In line 17
while(a[c]!=i)

You are using c as a subscript of an array for comparison.
So here you are actually comparing “while(a[-1]!=i)”

In C you cannot use negative subscript for an array(a[-1]) until here a represents a pointer pointing to the second or greater element.

Hope this helps.

4

i have corrected my mistake it ran correct for the testcases but it is now showing wrong ans… https://www.codechef.com/viewsolution/8802018

5

With the type of code you’ve written, there is little help you will find here except if you post your pseudocode. I just wrote a solution for the problem, and I think you might be able to understand it.
Ask any questions in the comments.

Pseudocode:

  1. Mark all indices as unvisited

  2. Find the lowest unvisited index i and store it in x (for future use)

  3. Visit the number at index i, and set i=a[i]

  4. Repeat 3 while a[i]!=x

  5. Goto 2, Exit if all indices visited.

Code:

#include <bits/stdc++.h>
using namespace std;
struct _ { ios_base::Init i; _() { cin.sync_with_stdio(0); cin.tie(0); } } _;

///////////////////////////////////////////////////////////////////////////////
	#define endl '\n'
	#define ll long long
	#define ld long double
	#define pb push_back
	#define mt make_tuple
	#define in(a) for (auto& i: a)
	#define tbeg clock_t _t=clock();
	#define test ll t; cin >> t; for (ll tc=1; tc<=t; tc++) {
	#define tend cout << "\n\nTime: " << (double)(clock()-_t)/CLOCKS_PER_SEC;
///////////////////////////////////////////////////////////////////////////////

ll pickindex(ll visited[], ll n)
{
	ll i;
	for (i=1; i<=n && visited[i]; i++);
	return i>n ? 0 : i;
}


int main()
{

	ll n, i, x, ctr=0;
	cin >> n;
	ll a[n+1], visited[n+1];
	in(visited) i=0;
	for (i=1; i<=n; i++) cin >> a[i];
	stringstream buffer;
	for (i=pickindex(visited, n); i; ctr++, i=pickindex(visited, n))
	{
		visited[i]=1;
		buffer << i << ' ';
		for (ll x=i; a[i]!=x; visited[a[i]]=1, i=a[i]) buffer << a[i] << ' ';
		buffer << a[i] << endl;
	}
	cout << ctr << endl << buffer.str();
}