Created
November 28, 2015 10:13
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yukicoder No.19
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#include <iostream> | |
#include <iomanip> | |
#include <vector> | |
#include <algorithm> | |
#include <numeric> | |
#include <functional> | |
#include <cmath> | |
#include <queue> | |
#include <stack> | |
#include <set> | |
#include <map> | |
#include <sstream> | |
#include <string> | |
#define repd(i,a,b) for (int i=(a);i<(b);i++) | |
#define rep(i,n) repd(i,0,n) | |
#define var auto | |
#define mod 1000000007 | |
#define inf 2147483647 | |
#define nil -1 | |
typedef long long ll; | |
using namespace std; | |
inline int input(){ | |
int a; | |
cin >> a; | |
return a; | |
} | |
template <typename T> | |
inline void output(T a, int p) { | |
if(p){ | |
cout << fixed << setprecision(p) << a << "\n"; | |
} | |
else{ | |
cout << a << "\n"; | |
} | |
} | |
// end of template | |
int main() { | |
cin.tie(0); | |
// source code | |
int N = input(); | |
vector<int> L(N), S(N); | |
vector<vector<int>> E(N, vector<int> (N)); // 有向辺E[to][from] | |
int ret = 0; | |
rep(to, N){ | |
L[to] = input(); | |
S[to] = input() - 1; | |
E[S[to]][to] = 1; | |
E[to][to] = 1; | |
ret += L[to]; | |
} | |
// ワーシャルフロイド | |
rep(k, N){ | |
rep(i, N){ | |
rep(j, N){ | |
E[i][j] |= E[i][k] && E[k][j]; | |
} | |
} | |
} | |
vector<int> vis(N, 0); | |
rep(i, N){ // 頂点0から順に辿っていく.もし頂点iを含む強連結成分に有向辺が伸びていないならば,その強連結成分について全て調べ,costがminなものを採用. | |
if (vis[i]) continue; | |
bool isRoot = true; | |
rep(j, N){ | |
if (E[j][i] && !E[i][j]) { | |
isRoot = false; | |
} | |
} | |
if (!isRoot) continue; | |
int tmp = inf; | |
rep(j, N){ | |
if (E[i][j] && E[j][i]) { | |
tmp = min(tmp, L[j]); | |
vis[j] = 1; | |
} | |
} | |
ret += tmp; | |
} | |
output((double)ret / 2.0, 1); | |
return 0; | |
} |
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