破环qwq
1 #include<cstdio> 2 #include<cstring> 3 #include<cstdlib> 4 #include<algorithm> 5 #include<iostream> 6 7 using namespace std; 8 9 void setIO(const string& s) { 10 freopen((s + ".in").c_str(), "r", stdin); 11 freopen((s + ".out").c_str(), "w", stdout); 12 } 13 template<typename Q> Q read(Q& x) { 14 static char c, f; 15 for(f = 0; c = getchar(), !isdigit(c); ) if(c == '-') f = 1; 16 for(x = 0; isdigit(c); c = getchar()) x = x * 10 + c - '0'; 17 if(f) x = -x; 18 return x; 19 } 20 template<typename Q> Q read() { 21 static Q x; read(x); return x; 22 } 23 typedef long long LL; 24 const int N = 2000000 + 10; 25 26 struct Edge { 27 int to; 28 Edge *next; 29 Edge() {} 30 Edge(int to, Edge *next) : to(to), next(next) {} 31 }pool[N * 2], *fir[N], *pis = pool; 32 33 void AddEdge(int u, int v) { 34 fir[u] = new(pis++) Edge(v, fir[u]); 35 fir[v] = new(pis++) Edge(u, fir[v]); 36 } 37 38 int r1, r2; 39 40 int val[N], vis[N], fa[N]; 41 42 void find_circle(int u) { 43 vis[u] = 1; 44 for(Edge *p = fir[u]; p; p = p->next) { 45 int v = p->to; 46 if(vis[v]) { 47 if(fa[v] != u && fa[u] != v) r1 = u, r2 = v; 48 }else fa[v] = u, find_circle(v); 49 } 50 } 51 52 LL d[N][2]; 53 54 int flag[N]; 55 int vis_sign; 56 57 void dfs(int u) { 58 flag[u] = vis_sign; 59 d[u][0] = 0; 60 d[u][1] = val[u]; 61 for(Edge *p = fir[u]; p; p = p->next) { 62 int v = p->to; 63 if((u == r1 && v == r2) || (u == r2 && v == r1)) continue; 64 if(flag[v] != vis_sign) { 65 dfs(v); 66 d[u][0] += max(d[v][0], d[v][1]); 67 d[u][1] += d[v][0]; 68 } 69 } 70 } 71 72 int main() { 73 #ifdef DEBUG 74 freopen("in.txt", "r", stdin); 75 freopen("out.txt", "w", stdout); 76 #endif 77 78 int n = read<int>(); 79 for(int u = 1; u <= n; u++) { 80 read(val[u]); 81 AddEdge(u, read<int>()); 82 } 83 84 LL res = 0; 85 86 for(int u = 1; u <= n; u++) if(!vis[u]) { 87 r1 = r2 = 0; 88 find_circle(u); 89 LL tmp = 0; 90 vis_sign = 1; 91 if(r1) { 92 dfs(r1), tmp = d[r1][0]; 93 vis_sign = 2, dfs(r2), tmp = max(tmp, d[r2][0]); 94 }else dfs(u), tmp = max(d[u][0], d[u][1]); 95 res += tmp; 96 } 97 98 printf("%lld ", res); 99 100 return 0; 101 }