UVA1025 A Spy in the Metro

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define se second
#define fs first
#define ll long long
#define CLR(x) memset(x,0,sizeof x)
#define MC(x,y) memcpy(x,y,sizeof(x))  
#define SZ(x) ((int)(x).size())
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1 
#define INF 1e9
typedef pair<int,int> P;
const double eps=1e-9;
const int maxnnode=11000;
const int maxn=100100;
const int mod=20071027;

int has_train[205][75][2],t[75];
int dp[205][75];
int n,T,m1,m2,M1,M2;


int main(){
    int Kase=1;
    while(~scanf("%d",&n)&&n){
        CLR(has_train);
        CLR(dp);
        scanf("%d",&T);
        for(int i=1;i<=n-1;i++) scanf("%d",&t[i]);
        scanf("%d",&m1);
        for(int i=1;i<=m1;i++)
        {
            scanf("%d",&M1);
            for(int j=1;j<=n-1;j++)
            {
                if(M1<=T) has_train[M1][j][0]=1;
                M1+=t[j];
            }
        }
        scanf("%d",&m2);
        for(int i=1;i<=m2;i++)
        {
            scanf("%d",&M2);
            for(int j=n-1;j>=1;j--)
            {
                if(M2<=T) has_train[M2][j+1][1]=1;
                M2+=t[j];
            }
        }
        dp[T][n]=0;
        for(int i=1;i<=n-1;i++) dp[T][i]=INF;
        for(int i=T-1;i>=0;i--)
        for(int j=1;j<=n;j++){
            dp[i][j]=dp[i+1][j]+1;
            if(j<n&&has_train[i][j][0]&&i+t[j]<=T) dp[i][j]=min(dp[i][j],dp[i+t[j]][j+1]);
            if(j>1&&has_train[i][j][1]&&i+t[j-1]<=T) dp[i][j]=min(dp[i][j],dp[i+t[j-1]][j-1]);
        }
        printf("Case Number %d: ",Kase++);
        if(dp[0][1]>=INF) printf("impossible\n");
        else printf("%d\n",dp[0][1]);
    }
    return 0;
}