UVA1025---A Spy in the Metro(简单dp)

dp[i][j]表示时刻i,在车站j,等待的最少时间

有3种方案:

等一分钟

往左搭车

往右搭车

/*************************************************************************
    > File Name: uva1025.cpp
    > Author: ALex
    > Mail: [email protected]
    > Created Time: 2015年05月25日 星期一 19时05分09秒
 ************************************************************************/

#include <functional>
#include <algorithm>
#include <iostream>
#include <fstream>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <queue>
#include <stack>
#include <map>
#include <bitset>
#include <set>
#include <vector>

using namespace std;

const double pi = acos(-1.0);
const int inf = 0x3f3f3f3f;
const double eps = 1e-15;
typedef long long LL;
typedef pair <int, int> PLL;

int dp[220][55];
int t_use[55];
vector <int> go[220][55];

int main() {
    int n, T, icase = 1, times;
    while (~scanf("%d", &n), n) {
        scanf("%d", &T);
        int m1, m2; // m1 : L to R, m2 : R to L
        for (int i = 1; i <= n - 1; ++i) {
            scanf("%d", &t_use[i]);
        }
        for (int i = 0; i <= T; ++i) {
            for (int j = 1; j <= n; ++j) {
                go[i][j].clear(); // time = i, station = j
            }
        }
        scanf("%d", &m1);
        for (int i = 1; i <= m1; ++i) {
            scanf("%d", &times);
            int t = times;
            if (t > T) {
                continue;
            }
            go[t][1].push_back(i);
            for (int j = 1; j <= n - 1; ++j) {
                t += t_use[j];
                if (t > T) {
                    break;
                }
                go[t][j + 1].push_back(i);
            }
        }
        scanf("%d", &m2);
        for (int i = 1; i <= m2; ++i) {
            scanf("%d", &times);
            int t = times;
            if (t > T) {
                continue;
            }
            go[t][n].push_back(i + m1);
            for (int j = n - 1; j >= 1; --j) {
                t += t_use[j];
                if (t > T) {
                    break;
                }
                go[t][j].push_back(i + m1);
            }
        }
        for (int i = 0; i <= T; ++i) {
            for (int j = 1; j <= n; ++j) {
                dp[i][j] = inf;
            }
        }
        dp[0][1] = 0;
        for (int i = 0; i < T; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (dp[i][j] == inf) {
                    continue;
                }
                int size = go[i][j].size();
                dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + 1);
                for (int k = 0; k < size; ++k) {
                    int u = go[i][j][k];
                    if (u <= m1 && j < n) {
                        if (i + t_use[j] <= T) {
                            dp[i + t_use[j]][j + 1] = min(dp[i + t_use[j]][j + 1], dp[i][j]);
                        }
                    }
                    else if (j > 1 && u > m1) {
                        if (i + t_use[j - 1] <= T) {
                            dp[i + t_use[j - 1]][j - 1] = min(dp[i + t_use[j - 1]][j - 1], dp[i][j]);
                        }
                    }
                }
            }
        }
        int ans = inf;
        for (int i = 0; i <= T; ++i) {
            if (dp[i][n] == inf) {
                continue;
            }
            ans = min(ans, dp[i][n] + T - i);
        }
        if (ans == inf) {
            printf("Case Number %d: impossible\n", icase++);
        }
        else {
            printf("Case Number %d: %d\n", icase++, ans);
        }
    }
    return 0;
}