POJ 2240 (SPFA判正环)

Posted 2022-07-29 jrfr

emmmmm又是SPFA没啥好讲的板子题

#include <iostream>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <map>
#include <iomanip>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <vector>
//const int maxn = 1e5+5;
#define ll long long
ll gcd(ll a,ll b)return b?gcd(b,a%b):a;
ll lcm(ll a,ll b)return a/gcd(a,b)*b;
//const int inf = 0x6fffffff;

#define MAX INT_MAX
#define FOR(i,a,b) for( int i = a;i <= b;++i)
#define bug cout<<"--------------"<<endl
using namespace std;
string s[35];
int ver[1100],next[1100],head[1100],ans[1100],vis[1100];
double edge[1100],d[1100];
int tot,n;
void add(int x,int y,double z)

    ver[++tot] = y,edge[tot] = z,next[tot] = head[x] , head[x] = tot;

int spfa(int first)

    memset(vis,0,sizeof(vis));
    memset(d,0,sizeof(d));
    memset(ans,0,sizeof(ans));
    d[first] = 10;
    vis[first] = 1;
    ans[first] ++;
    queue<int>que;
    que.push(first);
    while(que.size())
    
        int x = que.front();que.pop();
        vis[x] = 0;

//        cout<<x<<"       ";
//        FOR(i,1,3)
//        cout<<vis[i]<<" ";
//        cout<<endl;

        for(int i=head[x];i;i=next[i])
        
            int y = ver[i];
            double z = edge[i];
            // cout<<y<<" "<<d[y]<<" "<<d[x]*z<<endl;
            if(d[y] <(double) d[x] * z)
            

                d[y] =(double) d[x] * z;
                if(vis[y] == 1) continue;
                vis[y] = 1;
                que.push(y);
                ans[y]++;
                if(ans[y] >= n)
                
                    return 1;
                
            
        
    
    return 0;

void clearr()

    tot = 0;
    memset(head,0,sizeof(head));
    memset(next,0,sizeof(next));
    memset(ver,0,sizeof(ver));
    memset(edge,0,sizeof(edge));

int main()

//   freopen("C:\\Users\\方瑞\\Desktop\\input.txt","r",stdin);
//    freopen("C:\\Users\\方瑞\\Desktop\\output.txt","w",stdout);
    ios::sync_with_stdio(false);
    int casee=0;
    while((cin>>n) && n)
    
        clearr();
        FOR(i,1,n) cin>>s[i];
        int m;
        cin>>m;
        while(m--)
        
            string s1,s2;
            double hhh;
            cin>>s1>>hhh>>s2;
            int fx,fy;
            for(int i=1;i<=n;++i)
            
                if(s[i] == s1) fx = i;
                if(s[i] == s2) fy = i;
            
           // cout<<fx<<" "<<fy<<" "<<hhh<<endl;
            add(fx,fy,hhh);
        
        int flag = 0;
        for(int i=1;i<=n;++i)
        
            if(spfa(i) == 1)
            
                flag = 1;
                break;
            
        
        if(flag == 1) cout<<"Case "<<++casee<<": Yes"<<endl;
        else cout<<"Case "<<++casee<<": No"<<endl;