Travelling (三进制+状压dp)

题目链接

 #include <bits/stdc++.h>
 using namespace std;
 typedef long long ll;
 inline ll read(){
     int x=,f=;char ch=getchar();
     while(ch>''||ch<''){if(ch=='-')f=-;ch=getchar();}
     while(ch>=''&&ch<=''){x=x*+ch-'';ch=getchar();}
     return x*f;
 }

 /***********************************************************/

 int n, m;     // n < = 10
 const int maxn = 6e4+;
 int d[][maxn];
 //用三进制形式来表示状态
 int dist[][];
 //表示路径
 int t[];
 int cnt, state[maxn];
 int temp;

 //判断S的三进制是否没有一个0
 bool legal(int S){
     bool ok = true;
     for(int i = ;i <= n-;i++){
         if(S% == ){
             ok = false;
             break;
         }
         S /= ;
     }
     return ok;
 }

 void init(){
     temp = ;
     for(int i = ;i <= ;i++){
         t[i] = temp;
         temp *= ;
     }
 }

 //i点在集合S中是否出现了至少一次
 inline bool in(int i, int S){
     for(int j = ;j < i;j++)
         S /= ;
     if(S%) return true;
     else return false;
 }

 int dp(int i, int S){
     if(d[i][S] >= ) return d[i][S];
     int &ans = d[i][S];
     ans = 1e9;
     int S1 = S - t[i];
     for(int j = ;j < n;j++){
         if(j != i && in(j, S1) && dist[j][i] != -)
             ans = min(ans, dp(j, S1) + dist[j][i]);
     }
     return ans;
 }

 int main(){
     init();
     while(~scanf("%d %d", &n, &m)){
         int max_3 = ;
         for(int i = ;i < n;i++)
             max_3 += t[i];
         cnt = ;
         for(int S = max_3;S < t[n];S++){
             if(legal(S))
                 state[cnt++] = S;
         }
         memset(dist, -, sizeof(dist));
         for(int i = ;i < m;i++){
             int a, b, c;
             scanf("%d%d%d", &a, &b, &c);
             a--;b--;
             //更新长度
             if(dist[a][b] == - || dist[a][b] > c)
                 dist[a][b] = dist[b][a] = c;
         }
         memset(d, -, sizeof(d));
         for(int i = ;i < n;i++)
             d[i][t[i]] = ;

         int sum = dp(, max_3);
         for(int i = ;i < n;i++){
             for(int j = ;j < cnt;j++){
                 sum = min(sum, dp(i, state[j]));
             }
         }
         if(sum == 1e9) printf("-1\n");
         else printf("%d\n", sum);
     }
     return ;
 }