day 2 下午 骑士 基环树+树形DP

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<cstdlib>
  5 #include<algorithm>
  6 using namespace std;
  7 const int maxn=2e6+10;
  8 long long  dp[maxn][2];
  9 long long  w[maxn];
 10 
 11 struct node
 12 {
 13     long long  to,next,value;
 14 }way[maxn];
 15 long long tmp;
 16 long long tot;
 17 long long  n,x;
 18 long long  head[maxn];
 19 bool vis[maxn];
 20 long long  root;
 21 long long  father;
 22 long long  ans1,ans;
 23 int  read()       
 24 {
 25     int flag = 1;
 26     char c = getchar();
 27     while ((!isdigit(c)) && c != '-') c = getchar();
 28     if (c == '-') flag = -1, c = getchar();
 29     int init = c & 15;
 30     while (isdigit(c = getchar())) init = (init << 3) + (init << 1) + (c & 15);
 31     return init * flag;
 32 }
 33 void add(long long  x,long long  y,long long  w)
 34 {
 35     way[++tot].next=head[x];
 36     way[tot].to=y;
 37     way[tot].value=w;
 38     head[x]=tot;
 39 }
 40 void  dfs(long long  x,long long  fa)
 41 {
 42     vis[x]=1;
 43     for(int i=head[x];i;i=way[i].next)
 44     {
 45         long long  to=way[i].to;
 46         if(to==fa)
 47         {
 48             continue;
 49         }
 50         if(vis[to])
 51         {
 52             root=to;
 53             father=x;
 54             tmp=way[i].value;
 55         }
 56         else
 57         {
 58             dfs(to,x);    
 59         }
 60     }
 61 }
 62 void  shu_dp(long long  x,long long  fa)
 63 {
 64     dp[x][0]=0;
 65     dp[x][1]=w[x];
 66     for(int i=head[x];i;i=way[i].next)
 67     {
 68         long long  to=way[i].to;
 69         if(way[i].value==tmp||to==fa)
 70         {
 71             continue;
 72         }
 73         shu_dp(to,x);
 74         dp[x][0]+=max(dp[to][0],dp[to][1]);
 75         dp[x][1]+=dp[to][0];
 76     }
 77 }
 78 int main()
 79 {
 80     n=read();
 81     for(int i=1;i<=n;i++)
 82     {
 83         w[i]=read();
 84         x=read();
 85         add(i,x,i);
 86         add(x,i,i);
 87     }
 88     for(int i=1;i<=n;i++)
 89     {
 90         if(!vis[i])
 91         {
 92             dfs(i,0);
 93             shu_dp(root,0);
 94             ans1=dp[root][0];
 95             shu_dp(father,0);
 96             long long ans2;
 97             ans2=dp[father][0];
 98             ans1=max(ans1,ans2);
 99             ans+=ans1;
100         }
101     }
102     printf("%lld\n",ans);
103     return 0;
104 }