[HDOJ3538]A sample Hamilton path

经典问题：哈密尔顿路径 DP~

#include <cstdio>
#include <cstring>

 #define MIN(a,b) (a < b ? a : b)

 using namespace std;

const int NC = 20;
const int INF = (1 << 20);

int dp[1<<NC][NC];

int limit[NC];
int length[NC][NC];

int main()
{
    int nv;
    int nl;
    int va;
    int vb;

    while (scanf("%d %d",&nv,&nl) != EOF)
    {
        memset(limit,0,sizeof(limit));

        for (int i = 0;i < nv;i++)
            for (int j = 0;j < nv;j++)
                scanf("%d",&length[i][j]);

        for (int i = 0;i < nl;i++)
        {
            scanf("%d %d",&va,&vb);
            limit[vb] |= (1 << va);
        }

        int lim = (1 << nv);
        for (int i = 0;i < lim;i++)
            for (int j = 0;j < nv;j++)
                dp[i][j] = INF;

        dp[1][0] = 0;

        for (int i = 1;i < lim;i++)
            for (int j = 0;j < nv;j++)
                for (int k = 0;k < nv;k++)
                    if (!(i & (1 << k)) && length[j][k] != -1 && (i & limit[k]) == limit[k])
                        dp[i|(1<<k)][k] = MIN(dp[i|(1<<k)][k],dp[i][j] + length[j][k]);

        int ans = (1 << 20);
        for (int i = 0;i < nv;i++)
        {
            int tmp = dp[lim-1][i];
            if (ans > tmp)
                ans = tmp;
        }
        printf("%d\n",ans == INF ? -1 : ans);
    }
    return 0;
}