This is my program:

#include <stdio.h>
int len[16];
int ldist[16];
int rdist[16];
int depart;
int gor,gol,iv;
int N;
void prelr()
{
    int i;
    ldist[0]=0;
    for (i=1;i<N;i++)
        ldist[i]=ldist[i-1]+len[i-1];
    for (i=N-2;i>=0;i--)
        rdist[i]=rdist[i+1]+len[i];
}
void read()
{
    scanf("%d",&N);
    int i;
    for (i=0;i<N-1;i++)
        scanf("%d",&len[i]);
    scanf("%d",&depart);
    depart--;
    scanf("%d%d%d",&iv,&gor,&gol);
}
int best;
bool first;
int deptime;
void nexttimepoint(int&time,int&posi,int&dir)
{
    //Test nearest shuttle
    int tmp;
    if (dir==1)
    {
        tmp=((time-ldist[posi]-gor)%iv+iv)%iv;
        if (tmp!=0) tmp=iv-tmp;
        time+=tmp;
    }
    else
    {
        tmp=((time-rdist[posi]-gol)%iv+iv)%iv;
        if (tmp!=0) tmp=iv-tmp;
        time+=tmp;
    }
    //Record if it's first
    if (first)
    {
        first=false;
        deptime=time;
    }

    //Make path
    if (dir==1)
    {
        time+=len[posi];
        posi++;
    }
    else
    {
        time+=len[posi-1];
        posi--;
    }

    //Test if reverse needed
    if (posi==0)
        dir=1;
    if (posi==N-1)
        dir=-1;

}
void testdepart(int direct)
{
    int i,time,p,delayi,dir;
    int last;
    for (i=1<<(N-2);i-->0;)
    {
        delayi=i;
        last=(1<<N)-1;
        if (direct==1)
            time=ldist[depart];
        else
            time=rdist[depart];
        p=i;
        dir=direct;
        p=depart;
        first=true;
        nexttimepoint(time,p,dir);
        while (p!=depart||dir!=direct)
        {
            if (p==0||p==N-1)
                time++;
            else if (last&(1<<p)&&p!=depart)
            {
                if (delayi&(1<<(p-1)))
                    delayi^=1<<(p-1);
                else
                {
                    last^=1<<p;
                    time++;
                }
            }
            nexttimepoint(time,p,dir);
        }
        if (best>time-deptime)
            best=time-deptime;
    }
}
void process()
{
    prelr();
    if (depart!=N-1)
        testdepart(1);
    if (depart!=0)
        testdepart(-1);
}
int main()
{
    read();
    best=2147483647;
    if (N==1)
        printf("0\n");
    else
        process();
    printf("%d\n",best);
    return 0;
}

Thanks.

These two absolutely random test
based on my AC prog
6
7 6 3 2 8
3
12 56 34
res:96

12
1 2 45 64 31 23 128 61 2 2 7
8
11 1001 31
res:825

try test
1
1
100 100 100

answer is 0 :)

Edited by author 07.09.2010 23:23

Edited by author 07.09.2010 23:24

I think it`s wrong answer, because this need at least 1 train starting in 1, and it takes 1001 minutes, but your answer less than it.

Let then another AC authors apply their programs to
these tests

I understand, thanks

The interval between the trains is nonzero and doesn’t exceed 10^5, and the departure time from the terminal stations doesn’t exceed the interval.

In your tests it is not true.

Edited by author 01.04.2011 17:46

Edited by author 01.04.2011 17:46

Yes,
I solved problem with more wide conditions.
In my test  11 1001 31, and 1001,31>11.
But my algo (DP) allow such expansion.
So tests are useful. Solve problem in broader conditions
and get AC in narrow case.

can anyone tell me why the sample's answer is 28?

These two absolutely random test
based on my AC prog
6
7 6 3 2 8
3
12 56 34
res:96

12
1 2 45 64 31 23 128 61 2 2 7
8
11 1001 31
res:825

My AC program gives 156 and 1837 respectively. So... weak tests?

Edited by author 13.10.2014 19:33

These tests are wrong as "departure time from the terminal stations doesn’t exceed the interval." not trusted.