I will post one if I solve it.

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.

1. Problem model is not clear: whether train from station 1, after reaching station N, continues then moving in the opposite direction (station N -> station 1), or "disappears" after?
2. Another bug in statement: "You may assume that train stops at each station are instant." and "it takes one second to board a train". How these two statements relate to each other? If train stop is instant, how tourist can board it the whole 1 second???

Answers:
1. No, it "disappears" (which is very different from the real world)
2. This stupid statement is just to show that the tourist should stay on the station during 1 minute, i.e. he cannot leave on the same train he reached the station with

Edited by author 01.07.2014 00:38

"train stops at each station are instant" and "it takes one second to board a train".
So, the man spend one second to board a train, but the train do not stop for a second at the station.

Tourist can not get into train at time 0 - he must wait for another one. (I got WA 4, when missed this).

Why so few authors? Classic dp gets AC fast enough...

Excellent problem. Very realistic and DP works.
Small advice: We should consider moments after stationary
condition established: first trains went to last stations.
Without this we must include 10^5 moments in Dp and
will be MLE and TLE.

Edited by author 30.12.2007 10:32