POJ 3411 Paid Roads(DFS)

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题意你要从第1个城市到第N个城市去有m条路每条路用a, b, c, p, r 表示你从第a个城市到第b个城市时若之前经过或现在位于第c个城市过路费就是p元否则就是r元求你到达第N个城市最少用多少过路费

由于最多只有10个城市 10条路这个题就变得很简单了直接暴力dfs就行可以用状态压缩来存储已经走过了哪些城市由于最多只有10条路从某个城市出发要一条回这个城市也要一条所以一个城市最多经过5次这个可以作为dfs的结束条件

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int N = 11, INF = 2333333;int n, m, ans, vis[N];struct road{    int a, b, c, p, r;} rd[N];//当前所在城市, 到过哪些城市, 当前已经用了多少过路费void dfs(int p, int s, int v){    if(vis[p] > 5) return;    s = s | 1 << (p - 1);    if(p == n)    {        ans = min(ans, v);        return;    }    for(int i = 0; i < m; ++i)    {        if(rd[i].a != p) continue;        ++vis[rd[i].b];        if(s & 1 << (rd[i].c - 1)) //到过城市c            dfs(rd[i].b, s, v + rd[i].p);        else dfs(rd[i].b, s, v + rd[i].r);        --vis[rd[i].b]; //回溯    }}int main(){    while(~scanf("%d%d", &n, &m))    {        for(int i = 0; i < m; ++i)            scanf("%d%d%d%d%d", &rd[i].a, &rd[i].b, &rd[i].c, &rd[i].p, &rd[i].r);        ans = INF;        memset(vis, 0, sizeof(vis));        dfs(1, 0, 0);        if(ans == INF) puts("impossible");        else printf("%d\n", ans);    }    return 0;}

Paid Roads

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 a_i to city b_i:

in advance, in a city c_i (which may or may not be the same as a_i);
after the travel, in the city b_i.

The payment is P_i in the first case and R_i 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 a_i, b_i, c_i, P_i, R_i (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 ≤ P_i , R_i ≤ 100, P_i ≤ R_i (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 51 2 1 10 102 3 1 30 503 4 3 80 802 1 2 10 101 3 2 10 50

Sample Output

Source

Northeastern Europe 2002, Western Subregion

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