hdu3001_三进制状压dp

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3001

题意：n个城市， 每个城市最多去两次，起点任意，问需要的最少旅费是多少？

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <set>
#include <map>
#include <queue>
#include <vector>
#define INF 0x3f3f3f3f
using namespace std;

const int N = 10, M = 60100;
int dp[M][N];
int num[11][11], ab[11];
int n, m, f[M][N];
void find()
{
    ab[0] = 1;
    for(int i = 1; i <= 10; ++i)
        ab[i] = 3 * ab[i - 1];
    for(int i = 0; i < M; i++)
    {
        int te = i;
        for(int j = 0; j < N; j++)
        {
            f[i][j] = te % 3;
            te /= 3;
        }
    }
}
int rec()
{
    int sum = ab[n];
    for(int i = 0; i < sum; ++i)
        for(int j = 0; j < n; ++j)
            dp[i][j] = INF;
    for(int i = 0; i < n; i++)
        dp[ab[i]][i] = 0;
    for(int i = 1; i < sum; ++i)
    {
        for(int j = 0; j < n; ++j)
        {
            if(dp[i][j] == INF)
                continue;
            if(f[i][j] != 0)
            {
                for(int k = 0; k < n; ++k)
                {
                    if(f[i][k] == 2 || k == j || num[j][k] == INF)
                        continue;     
                    int next = i + ab[k];
                    dp[next][k] = min(dp[next][k], dp[i][j] + num[j][k]);
                }
            }
        }
    }
    int res = INF, s1 = 1, first = 0;     
    for(int i = 0; i < n; ++i)   
    {
        first += s1;  
        s1 *= 3;          
    }
    for(int i = first; i < sum; ++i)
    {
        int ok = 1;
        for(int j = 0; j < n; j++)//判断是否有城市没去过
        {
            if(f[i][j] == 0)
            {
                ok = 0;
                break;
            }
        }
        if(ok)
            for(int k = 0; k < n; ++k)
                res = min(dp[i][k], res);
    }
    return res;
}
int main()
{
    int a, b, c;
    find();
    while(~scanf("%d %d", &n, &m))
    {
        for(int i = 0; i < n; ++i)
            for(int j = 0; j < n; ++j)
                num[i][j] = INF;
        for(int i = 0; i < m; ++i)
        {
            scanf("%d %d %d", &a, &b, &c);//还要判断重边
            num[a - 1][b - 1] = num[b - 1][a - 1] = min(c, num[a - 1][b - 1]);
        }
        int res = rec();                        
        if(res == INF)
            printf("-1
");
        else
            printf("%d
", res);
    }
    return 0;
}