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poj 3411 Paid Roads（dfs）

2024-07-29 08:25:53   222人阅读

Paid Roads
Time Limit: 1000MS Memory Limit: 65536K
Total Submissions: 5481 Accepted: 1947

Description

A network of m roads connects N cities (numbered from 1 to N). There may be more than one road connecting one city with another. Some of the roads are paid. There are two ways to pay for travel on a paid road i from city ai to city bi:

  • in advance, in a city ci (which may or may not be the same as ai);
  • after the travel, in the city bi.

The payment is Pi in the first case and Ri in the second case.

Write a program to find a minimal-cost route from the city 1 to the city N.

Input

The first line of the input contains the values of N and m. Each of the following m lines describes one road by specifying the values of ai, bi, ci, Pi, Ri (1 ≤ i ≤ m). Adjacent values on the same line are separated by one or more spaces. All values are integers, 1 ≤ m, N ≤ 10, 0 ≤ Pi , Ri ≤ 100, Pi ≤ Ri (1 ≤ i ≤ m).

Output

The first and only line of the file must contain the minimal possible cost of a trip from the city 1 to the city N. If the trip is not possible for any reason, the line must contain the word ‘impossible’.

Sample Input

4 5
1 2 1 10 10
2 3 1 30 50
3 4 3 80 80
2 1 2 10 10
1 3 2 10 50

Sample Output

110


有n个城市m条路线，每条路线有5个值，a,b,c,p,r表示从a城到b城，如果到过c城，收费p元，否则收费r元。现在从1到n，求最小花费。

这题主要是去过的点又回来的问题，例如样例1->2->1->3->4，从2又返回了1，由于m=10，所以一个点最多访问3次(其实取2也能A，感觉还是3靠谱点）

ps：刚开始记录了map[i][j]表示i到j可以走第map[i][j]条路，因为从第i到j可以有多条路，一直wa，再改就麻烦了，换成直接枚举m条路，反正m也不大。

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int inf=99999999;
//int map[15][15];
int vis[15];
int n,m;
int ans;
struct node
{
    int a;
    int b;
    int c;
    int p;
    int r;
}road[15];
void dfs(int u,int v)
{
    if(v>ans)
    return;
    if(u==n)
    {
        if(v<ans)
        {
           ans=v;
          // printf("  %d\n",ans);
        }
        return;
    }
    for(int i=1;i<=m;i++)
    {
        if(road[i].a==u&&vis[road[i].b]<=3)
        {
            int b=road[i].b;
            vis[b]++;
            if(vis[road[i].c])
            {
                dfs(b,v+road[i].p);
            }
            else
            {
               dfs(b,v+road[i].r);
            }
            vis[b]--;
        }
    }
    return;
}
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        memset(vis,0,sizeof(vis));
        ans=inf;
        for(int i=1;i<=m;i++)
        {
            scanf("%d%d%d%d%d",&road[i].a,&road[i].b,&road[i].c,&road[i].p,&road[i].r);
        }
        vis[1]=1;
        dfs(1,0);
        if(ans==inf)
        printf("impossible\n");
        else
        printf("%d\n",ans);
    }
    return 0;
}



poj 3411 Paid Roads（dfs）


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