NOIP 2017 d2t2 70points

革命之路漫漫

第一次尝试 40points spfa

 #include <bits/stdc++.h>
 #define read read()
 using namespace std;

 inline int 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;
 }

 const int N = ;

 struct edge{
     int v,nxt,w;
 }e[N<<];

 int n,m;
 int head[N],size;
 int dis[N],vis[N],maxn = INT_MAX;
 void add(int u,int v,int w)
 {
     e[++size].v = v;
     e[size].w = w;
     e[size].nxt = head[u];
     head[u] = size;
 }

 queue<int>q;

 void spfa(int s)
 {
     memset(dis,0x3f,sizeof(dis));
     memset(head,,sizeof());
     memset(vis,,sizeof(vis));
     dis[s] = ;
     q.push(s);
     vis[s] = ;
     while(!q.empty())
     {
         int u = q.front(); q.pop(); vis[u] = ;
         for(int i = head[u]; i ; i = e[i].nxt)
         {
             int v = e[i].v, w = e[i].w;
             if(dis[v] > dis[u] + )
             {
                 dis[v] = dis[u] + ;
                 if(!vis[v])
                 {
                     q.push(v);
                     vis[v] = ;
                 }
             }
         }
     }
 }

 int main()
 {
     freopen("treasure.in","r",stdin);
     n = read; m = read;
     int u,v,w;
     for(int i = ; i <= m; i++)
     {
         u = read; v = read; w = read;
         add(u,v,w);
         add(v,u,w);     }
     for(int i = ; i <= n; i++)
     {
         spfa(i);
         int ans = ;
         for(int i = ; i <= n; i++)
         {
             ans += dis[i] * w;
         }
         maxn = min(maxn , ans);
     }
     printf("%d",maxn);
     return ;
 }

第二次尝试 dfs

 #include <bits/stdc++.h>
 #define read read()
 using namespace std;

 const int N = ;

 int n,m;
 int cost[N][N],cnt[N];
 int head[N],size;
 int ans = INT_MAX, mincost;
 int read
 {
     int x = ; char ch = getchar();
     while(ch <  || ch > ) ch = getchar();
     while(ch >= && ch <= ) { x =  * x + ch - ; ch = getchar();}
     return x;
 }

 void dfs(int cur)//暴力枚举所有情况;
 {
     if(cur == n)
     {
         ans = min(ans,mincost);
         return;
     }
     if(mincost > ans) return;
     for(int i = ; i <= n; i++) //枚举出点;
     {
         if(!cnt[i]) continue;   //还未连通的点不能当作出点;
         for(int j = ; j <= n; j++) //枚举入点;
         {
             if(i == j || cnt[j] || cost[i][j] == 0x3f3f3f3f) continue;
             mincost += cnt[i] * cost[i][j];
             cnt[j] = cnt[i] + ;
             dfs(cur + );
             mincost -= cnt[i] * cost[i][j];
             cnt[j] = ;
         }
     }
 }

 int main()
 {
 //    freopen("treasure.in","r",stdin);
     n = read;m = read;
     memset(cost,0x3f,sizeof(cost));
     int u,v;
     for(int i = ; i <= m; i++)
     {
         u = read; v = read;
         cost[u][v] = cost[v][u] = min(read , cost[u][v]);         //细节: u-v之间可能有多条路连接, 忽略其余选最短;
     }
     for(int i = ; i <= n; i++) //枚举起点;
     {
         cnt[i] = ;
         dfs();
         cnt[i] = ;
     }
     printf("%d",ans);
     return ;
 }