POJ 2240 && ZOJ 1082 Arbitrage 最短路,c++ stl pass g++ tle 难度:0

时间:2021-03-22 10:11:41

http://poj.org/problem?id=2240

用log化乘法为加法找正圈

c++ 110ms,g++tle

#include <string>
#include <map>
#include <iostream>
#include <cmath>
#include <cstring>
#include <queue>
using namespace std;
const int maxn = 50;
bool vis[maxn];
double chg[maxn][maxn];
double dis[maxn];
int e[maxn][maxn],deg[maxn];
map<string,int> idmp;
int n,m;
const double inf = 0x3fffffff; queue<int> que;
bool hasloop(int s){
while(!que.empty())que.pop();
que.push(s);
vis[s] = true;
int cnt = 0;
while(!que.empty()){
cnt ++;
s = que.front();que.pop();vis[s] = false;
for(int i = 0;i < deg[s];i++)
{
int t = e[s][i];
if(dis[t] < dis[s] + chg[s][t])
{
dis[t] = dis[s] + chg[s][t];
que.push(t);
vis[t] = true;
}
}
if(cnt > n * n)return true;
}
return false;
} int main(){
int ti = 0;
while(cin>>n && n && ++ti){
idmp.clear();
for(int i = 0;i < n;i++)
{
dis[i] = -inf;
for(int j = 0;j < n;j++)chg[i][j] = -inf;
}
memset(vis,false,sizeof vis);
memset(deg,0,sizeof deg); for(int i = 0;i < n;i++)
{
string tmp;
cin>>tmp;
idmp[tmp] = i;
}
cin>>m;
for(int i = 0;i < m;i++)
{
string sf,st;
double change;
cin>>sf>>change>>st;
change = log(change);
int f = idmp[sf];
int t = idmp[st];
chg[f][t] = change;
e[f][deg[f]++] = t;
}
bool fl = false;
for(int i = 0;i < n;i++)
{
if(dis[i] == -inf){
dis[i] = 1;
if(hasloop(i)){
fl = true;
break;
}
}
}
cout << "Case " << ti << ": ";
if(fl)cout << "Yes" <<endl;
else cout << "No" << endl;
}
return 0;
}