E.Perpetuum Mobile
找正环，由于是乘法，所以用log变成加法，还有这题其实是看爱因斯坦那句话，和他助手说的没什么关系，所以要找一个环，环上的乘积大于1，即log >0。于是用spfa判正环就行了。
#include <algorithm> #include <iterator> #include <iostream> #include <cstring> #include <cstdlib> #include <iomanip> #include <bitset> #include <cctype> #include <cstdio> #include <string> #include <vector> #include <stack> #include <cmath> #include <queue> #include <list> #include <map> #include <set> #include <cassert> //#include <unordered_map> /* ⊂_ヽ ＼＼ Λ＿Λ 来了老弟 ＼('ㅅ') > ⌒ヽ / へ＼ / / ＼＼ ﾚ ノ ヽ_つ / / / /| ( (ヽ | |、＼ | 丿 ＼ ⌒) | | ) / 'ノ ) Lﾉ */ using namespace std; #define lson (l , mid , rt << 1) #define rson (mid + 1 , r , rt << 1 | 1) #define debug(x) cerr << #x << " = " << x << "\n"; #define pb push_back #define pq priority_queue typedef long long ll; typedef long double ld; typedef unsigned long long ull; //typedef __int128 bll; typedef pair<ll ,ll > pll; typedef pair<int ,int > pii; typedef pair<int,pii> p3; //priority_queue<int> q;//这是一个大根堆q //priority_queue<int,vector<int>,greater<int> >q;//这是一个小根堆q #define fi first #define se second //#define endl '\n' #define boost ios::sync_with_stdio(false);cin.tie(0) #define rep(a, b, c) for(int a = (b); a <= (c); ++ a) #define max3(a,b,c) max(max(a,b), c); #define min3(a,b,c) min(min(a,b), c); const ll oo = 1ll<<17; const ll mos = 0x7FFFFFFF; //2147483647 const ll nmos = 0x80000000; //-2147483648 const int inf = 0x3f3f3f3f; const ll inff = 0x3f3f3f3f3f3f3f3f; //18 const int mod = 998244353; const double esp = 1e-8; const double PI=acos(-1.0); const double PHI=0.61803399; //黄金分割点 const double tPHI=0.38196601; template<typename T> inline T read(T&x){ x=0;int f=0;char ch=getchar(); while (ch<'0'||ch>'9') f|=(ch=='-'),ch=getchar(); while (ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar(); return x=f?-x:x; } inline void cmax(int &x,int y){if(x<y)x=y;} inline void cmax(ll &x,ll y){if(x<y)x=y;} inline void cmin(int &x,int y){if(x>y)x=y;} inline void cmin(ll &x,ll y){if(x>y)x=y;} #define MODmul(a, b) ((a*b >= mod) ? ((a*b)%mod + 2*mod) : (a*b)) #define MODadd(a, b) ((a+b >= mod) ? ((a+b)%mod + 2*mod) : (a+b)) /*-----------------------showtime----------------------*/ typedef pair<int,double> pid; const int maxn = 1e3+9; vector<pid>mp[maxn]; int vis[maxn]; double dis[maxn]; queue<int>que; bool spfa(int u){ vis[u] = true; for(int i=0; i<mp[u].size(); i++){ pid tmp = mp[u][i]; int v = tmp.fi; double w = tmp.se; if(dis[v] < dis[u] + w){ dis[v] = dis[u] + w; if(vis[v]) return true; if(spfa(v)) return true; } } vis[u] = false; return false; } int main(){ int n,m; scanf("%d%d", &n, &m); rep(i, 1, m) { int u,v; double e; scanf("%d%d%lf", &u, &v, &e); mp[u].pb(pid(v, log(e))); } for (int i = 1; i <= n; ++i) if(spfa(i)) return 0*puts("inadmissible"); puts("admissible"); return 0; }