【POJ 1860】 Currency Exchange

【POJ 1860】 Currency Exchange

模拟货比交易 输入数据n 货币种类 m 交易种类 s 初始货币类型 v 初始持币数

m行分别为 A B(该种交易的两种货币A、B) RAB, CAB, RBA ,CBA A->B和B->A的交易汇率和手续费 交易后金额为(s-c)*r

最短路模板题 遍历看是否有正环(即可无限增加资本)

写了两种做法 SPFA比BellMan耗时长 可啪

SPFA

#include <cstdio>
#include <vector>
#include <queue>
#include <cstring>
#define esp 1e-8

using namespace std;

typedef struct Edge
{
    int v;
    double r,c;
}Edge;

Edge eg;
double dis[111];
int in[111];
bool vis[111];
vector <Edge> vct[111];
int n,m,s;

int dcmp(double x)
{
    return x < -esp? -1: x > esp;
}

bool SPFA(double st)
{
    memset(dis,0,sizeof(dis));
    memset(in,0,sizeof(in));
    dis[s] = st;
    queue <int> q;
    q.push(s);
    int i,x,u,v;
    double c,r;
    while(!q.empty())
    {
        u = q.front();
        q.pop();
        vis[u] = 0;
        for(i = 0; i < vct[u].size(); ++i)
        {
            v = vct[u][i].v;
            c = vct[u][i].c;
            r = vct[u][i].r;
            if(dcmp(dis[v] - (dis[u]-c)*r) < 0)
            {
                dis[v] = (dis[u]-c)*r;
                if(!vis[v])
                {
                    in[v]++;
                    if(in[v] > n) return true;
                    q.push(v);
                    vis[v] = 1;
                }
            }
        }
    }
    return false;
}

int main()
{
    int i,u,v;
    double sum;
    scanf("%d %d %d %lf",&n,&m,&s,&sum);
    for(i = 0; i < m; ++i)
    {
        scanf("%d %d %lf %lf",&u,&v,&eg.r,&eg.c);
        eg.v = v;
        vct[u].push_back(eg);
        scanf("%lf %lf",&eg.r,&eg.c);
        eg.v = u;
        vct[v].push_back(eg);
    }
    if(SPFA(sum)) printf("YES\n");
    else printf("NO\n");
    return 0;
}

BellMan-Ford

#include <cstdio>
#include <vector>
#include <cstring>
#define esp 1e-8

using namespace std;

typedef struct Edge
{
    int u,v;
    double r,c;
}Edge;

Edge eg;
double dis[111];
vector <Edge> vct;
int n,m,s;

int dcmp(double x)
{
    return x < -esp? -1: x > esp;
}

bool BellMan_Ford(double st)
{
    memset(dis,0,sizeof(dis));
    dis[s] = st;
    int i,j,k,u,v,f;
    double r,c;
    for(i = 1; i < n; ++i)
    {
        f = 0;
        for(j = 0; j < vct.size(); ++j)
        {
            u = vct[j].u;
            v = vct[j].v;
            r = vct[j].r;
            c = vct[j].c;
            if(dcmp(dis[v] - (dis[u]-c)*r) < 0)
            {
                dis[v] = (dis[u]-c)*r;
                f = 1;
            }
        }
        if(!f) return false;
    }

    for(j = 0; j < vct.size(); ++j)
    {
        u = vct[j].u;
        v = vct[j].v;
        r = vct[j].r;
        c = vct[j].c;
        if(dcmp(dis[v] - (dis[u]-c)*r) < 0)
        {
            return true;
        }
    }

    return false;
}

int main()
{
    int i,u,v;
    double sum;
    scanf("%d %d %d %lf",&n,&m,&s,&sum);
    for(i = 0; i < m; ++i)
    {
        scanf("%d %d %lf %lf",&u,&v,&eg.r,&eg.c);
        eg.v = v;
        eg.u = u;
        vct.push_back(eg);
        scanf("%lf %lf",&eg.r,&eg.c);
        eg.v = u;
        eg.u = v;
        vct.push_back(eg);
    }
    if(BellMan_Ford(sum)) printf("YES\n");
    else printf("NO\n");
    return 0;
}