URAL1389. Roadworks（dp)

1389

算个简单的树形DP吧 不知道是不是数据太水 竟然一A了

就是对于当前节点有没有被选中就行选最优 有没有被选中的意思是有没有与它相连的边被选中

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 using namespace std;
 #define N 100010
 vector<int>d[N];
 int dp[N][],g;
 struct node
 {
     int u,v;
 }p[N];
 int dfs(int u,int v,int f)
 {
     if(dp[v][f]!=-)
     return dp[v][f];
     int i;
     int s[][] = {};
     int flag =,x=-;
     for(i =  ; i < d[v].size() ; i++)
     {
         int tv = d[v][i];
         if(tv==u) continue;
         flag = ;
         int s1 = dfs(v,tv,);
         if(f)
         {
             s[(i+)%][] = s[i%][]+s1;
         }
         else
         {
             int s2 = dfs(v,tv,)+;
             s[(i+)%][] = s[i%][]+s1;
             if(s[i%][]+s1<s[i%][]+s2)
             {
                 s[(i+)%][] = s[i%][]+s2;
                 x = tv;
             }
             else
             s[(i+)%][] = s[i%][]+s1;
         }
     }
     if(!flag)
     {
         return dp[v][f] = ;
     }
     if(x!=-)
     {
         g++;
         p[g].u = v;
         p[g].v = x;
     }
     int maxz = ;
     for(i =  ; i <  ; i++)
     maxz = max(maxz,max(s[][i],s[][i]));
     return dp[v][f] = maxz;
 }
 int main()
 {
     int i,n,m;
     while(cin>>n>>m)
     {
         memset(dp,-,sizeof(dp));
         for(i =  ; i <= n ;i++)
         d[i].clear();
         for(i = ; i <= m ;i++)
         {
             int u,v;
             cin>>u>>v;
             d[u].push_back(v);
             d[v].push_back(u);
         }
         dfs(-,,);
         cout<<dp[][]<<endl;
         for(i = ; i <= g ; i++)
         cout<<p[i].u<<" "<<p[i].v<<endl;
     }
     return ;
 }