[ZJOI2008]骑士

  1 #include<cstdio>
  2 #include<iostream>
  3 #include<cmath>
  4 #include<algorithm>
  5 #include<cstring>
  6 #include<cstdlib>
  7 #include<cctype>
  8 #include<vector>
  9 #include<stack>
 10 #include<queue>
 11 using namespace std;
 12 #define enter puts("") 
 13 #define space putchar(‘ ‘)
 14 #define Mem(a, x) memset(a, x, sizeof(a))
 15 #define rg register
 16 typedef long long ll;
 17 typedef double db;
 18 const int INF = 0x3f3f3f3f;
 19 const db eps = 1e-8;
 20 const int maxn = 1e6 + 5;
 21 inline ll read()
 22 {
 23     ll ans = 0;
 24     char ch = getchar(), last = ‘ ‘;
 25     while(!isdigit(ch)) {last = ch; ch = getchar();}
 26     while(isdigit(ch)) {ans = (ans << 1) + (ans << 3) + ch - ‘0‘; ch = getchar();}
 27     if(last == ‘-‘) ans = -ans;
 28     return ans;
 29 }
 30 inline void write(ll x)
 31 {
 32     if(x < 0) x = -x, putchar(‘-‘);
 33     if(x >= 10) write(x / 10);
 34     putchar(x % 10 + ‘0‘);
 35 }
 36 
 37 int n, a[maxn];
 38 
 39 struct Edge
 40 {
 41     int nxt, to;
 42 }e[maxn << 1];
 43 int head[maxn], ecnt = -1;
 44 void addEdge(int x, int y)
 45 {
 46     e[++ecnt] = (Edge){head[x], y};
 47     head[x] = ecnt;
 48 }
 49 
 50 int rt1, rt2, E;        //E, E ^ 1:the edge wich is cutted
 51 bool vis[maxn], cir[maxn];
 52 void Find(int now, int _e)
 53 {
 54     vis[now] = cir[now] = 1;
 55     for(int i = head[now], v; i != -1; i = e[i].nxt)
 56     {
 57         v = e[i].to;
 58         if(cir[v] && i != (_e ^ 1))
 59         {
 60             rt1 = now; rt2 = v; E = i;
 61         }
 62         if(!vis[v]) Find(v, i);
 63     }
 64     cir[now] = 0;
 65 }
 66 
 67 ll dp[maxn][2];
 68 void dfs(int now, int f)
 69 {
 70     dp[now][0] = dp[now][1] = 0;
 71     for(int i = head[now], v; i != -1; i = e[i].nxt)
 72     {
 73         v = e[i].to;
 74         if(v == f || i == E || i == (E ^ 1)) continue;
 75         dfs(v, now);
 76         dp[now][1] += dp[v][0];
 77         dp[now][0] += max(dp[v][1], dp[v][0]);
 78     }
 79     dp[now][1] += a[now];
 80 }
 81 
 82 int main()
 83 {
 84     Mem(head, -1);
 85     n = read();
 86     for(int i = 1; i <= n; ++i)
 87     {
 88         a[i] = read(); 
 89         int x = read(); addEdge(i, x); addEdge(x, i);
 90     }
 91     ll ans = 0;
 92     for(int i = 1; i <= n; ++i) if(!vis[i])
 93     {
 94         Find(i, -1);
 95         dfs(rt1, 0);
 96         ll Max = 0;
 97         if(dp[rt1][0] > Max) Max = dp[rt1][0];
 98         dfs(rt2, 0);
 99         if(dp[rt2][0] > Max) Max = dp[rt2][0];
100         ans += Max;
101     }
102     write(ans), enter;
103     return 0;
104 }