Getting WA with my STL code, but equivalent C code accepted

general
,
1

I was solving a pretty simple question trying to use STL for the first time.
The question was - http://www.codechef.com/problems/LEEXAMS/

I made a code using C++ along with some STL concepts which I recently learnt.
I would be grateful if someone would please tell me what is wrong in the code because of which I’m getting a wrong answer!

My code:

#include< iostream >
#include< algorithm >
#include< vector >
#include< stdio.h >
#include< set >
using namespace std;

vector<int> A,B,P;
set<int> used;
double ans;
int n;
void calc(int itr,double prob)
{
    if(itr==n)
    {
        ans+=prob;
        return;
    }
    //for A values
    if(P[itr]!=0)
    {
        pair<set<int>::iterator,bool> pa;
        pa = used.insert(A[itr]);           //try to insert the value
        if(pa.second==true)                //if a new value is inserted, that means it wasn't already present
        {
               calc(itr+1,prob*((double)P[itr])/100); //so go through with the chain of recursion
               used.erase(pa.first);        //and when you come out, remove the value just added using the iterator to the value
        }
    }
    //for B values
    if(P[itr]!=100)
    {
        pair<set<int>::iterator,bool> pa;
        pa = used.insert(B[itr]);           //try to insert the value
        if(pa.second==true)                //if a new value is inserted, that means it wasn't already present
        {
               calc(itr+1,prob*((double)(100-P[itr])/100)); //so go through with the chain of recursion
               used.erase(pa.first);        //and when you come out, remove the value just added using the iterator to the value
        }
    }
}

int main()
{
    int T,a,b,p;
    used.insert(0);
    scanf("%d",&T);
    while(T--)
    {
        ans=0.0;
        scanf("%d",&n);

            for(int i=1;i<=n;i++)
            {
                scanf("%d%d%d",&p,&a,&b);
                A.push_back(a);
                B.push_back(b);
                P.push_back(p);
            }
        if(n<=16)
        {
            calc(0,1);
            A.clear();B.clear();P.clear();
        }
        printf("%.14f\n",ans);
    
    }
    return 0;

}

Kind of Similar code in C which is accepted:


#include < stdio.h >
 
int n=0;
double out=0;
 
void sol(int A[27],int B[27], int P[27],int flag[27],int pos,double ans)
{	
	if(pos==n)
	{
		//printf("%lf\n",ans);
		out = out + ans;
		return ;	
	}
	else
	{
		if(!flag[A[pos]-1])
		{
			flag[A[pos]-1] = 1;
			sol(A,B,P,flag,pos+1,ans*P[pos]*flag[A[pos]-1]/100);
			flag[A[pos]-1] = 0;				
		}
		if(!flag[B[pos]-1])
		{
			flag[B[pos]-1] = 1;
			sol(A,B,P,flag,pos+1,ans*(100-P[pos])*flag[B[pos]-1]/100);
			flag[B[pos]-1] = 0;
		}		
	}
}
 
int main()
{
	int t,A[27],B[27],P[27],i;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%d",&n);
		for(i=0;i<n;i++)
				scanf("%d%d%d",P+i,A+i,B+i);
		if(n>16)
			out=0.0;
		else
		{
			int flag[27]={0};
			out = 0.0;			
			sol(A,B,P,flag,0,1.0);			
		}
		printf("%.14lf\n",out);
	}
	return 0;
	}

As far as I can tell, the concept used should work(regardless of how inefficient it may be), but I’m getting wrong answer.

Please help me out.