Uva 1025 A Spy in the Metro

/*---dp[i][j]表示i时刻在j站还需要等待的时间
----边界条件dp[T][n]=0,dp[T][1...n-1]=INF;
得到dp[i][j]有如下三种决策：
 1)时刻在j站等待一分钟
 2)搭乘向右的车(如果有)
 3)搭乘向左的车(如果有)
 ---初始化has[i][j][0]表示i时刻在j站是否有向右的车
 ---初始化has[i][j][1]表示i时刻在j站是否有向左的车
*/
#define _CRT_SECURE_NO_DEPRECATE
#include<iostream>
#include<vector>
#include<string.h>
#include<algorithm>
using namespace std;
#define INF 0x3f3f3f3f
typedef long long LL;
const int MAXN = 50 + 10;
int a[MAXN];
int b[MAXN];
int has[200 + 10][MAXN][2];
int t[MAXN];
int dp[200 + 10][MAXN];
int n, m1, m2,T;
bool vis[200 + 10][MAXN];
//记忆化搜索
int dfs(int i, int j){
	int &ans = dp[i][j];
	if (vis[i][j])
		return ans;
	vis[i][j] = 1;
	ans = dfs(i + 1, j) + 1;   //等待一分钟
	if (j<n&&(i + t[j])<= T&&has[i][j][0])
		ans = min(ans, dfs(i + t[j], j + 1));
	if (j>1 && i + t[j - 1] <= T&&has[i][j][1])
		ans = min(ans, dfs(i + t[j - 1], j - 1));
	return ans;
}
int main(){
	int i, j,iCase=1;
	while (scanf("%d", &n) && n){
		scanf("%d", &T);   
		for (i = 1; i < n; i++)
			scanf("%d", &t[i]);
		t[n] = t[0] = 0;
		scanf("%d", &m1);
		for (i = 1; i <=m1; i++)
			scanf("%d", &a[i]);
		scanf("%d", &m2);
		for (i = 1; i <= m2; i++)
			scanf("%d", &b[i]);

		memset(has, 0, sizeof(has));

		for (i = 1; i <= m1; i++){
			int p = a[i];
			for (j = 1; j <= n; j++){
				p += t[j - 1];
				if (p > T)
					break;
				has[p][j][0] = 1;
			}
		}

		for (i = 1; i <= m2; i++){
			int p = b[i];
			for (j =n; j>0; j--){
				p += t[j];
				if (p > T)
					break;
				has[p][j][1] = 1;
			}
		}
		memset(dp[T], 0x3f, sizeof(dp[T]));
		dp[T][n] = 0;
		memset(vis, 0, sizeof(vis));
		for (i = 1; i <=n; i++)
			vis[T][i] = 1;
		dp[0][1] = dfs(0, 1);
		printf("Case Number %d: ", iCase++);
		if (dp[0][1] >= INF)
			printf("impossible\n");
		else
			printf("%d\n", dp[0][1]);
	}
	return 0;
}