POJ 1860 & ZOJ 1544 Currency Exchange（最短路SPFA）

标签：poj   zju   最短路   spfa   

题目链接：

ZJU:http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=1544

PKU:http://poj.org/problem?id=1860

Description

Input

Output

Sample Input

3 2 1 20.0
1 2 1.00 1.00 1.00 1.00
2 3 1.10 1.00 1.10 1.00

Sample Output

YES

Source

代码如下：

#include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <ctype.h>
#include <queue>
#include <stack>
#include <vector>
#include <deque>
#include <set>
#include <map>
#include <iostream>
#include <algorithm>
using namespace std;
#define pi acos(-1.0)
#define INF 0xffffff
#define N 3005
#define M 2005
int Edgehead[N];
int cont[N];
double dis[N];
struct
{
    int v,next;
    double rate, comm, w;
} Edge[2*M];
bool vis[N];
int k;
int n, m, s;
double val;
void Addedge(int u,int v,double r, double c)
{
    Edge[k].next = Edgehead[u];
    Edge[k].rate = r;
    Edge[k].v = v;
    Edge[k].comm = c;
    Edge[k].w = 0;
    Edgehead[u] = k++;
}
void init()
{
    for(int i = 1 ; i <=n ; i++ )//求最长路径开始设为-1
        dis[i] = 0;
    memset(Edgehead,-1,sizeof(Edgehead));
    memset(vis,false,sizeof(vis));
    memset(cont,0,sizeof(cont));
}

int SPFA( int start)
{
    queue<int>Q;
    dis[start] = val;
    vis[start] = true;
    ++cont[start];
    Q.push(start);
    while(!Q.empty())//直到队列为空
    {
        int u = Q.front();
        Q.pop();
        vis[u] = false;
        for(int i = Edgehead[u] ; i!=-1 ; i = Edge[i].next)//注意
        {
            int v = Edge[i].v;
            Edge[i].w = (dis[u] - Edge[i].comm)*Edge[i].rate-dis[u];
            if(dis[v] < dis[u] + Edge[i].w)
            {
                dis[v] = dis[u]+Edge[i].w;
                if( !vis[v] )//防止出现环，也就是进队列重复了
                {
                    Q.push(v);
                    vis[v] = true;
                }
                if(++cont[v] > n)//有负环
                    return -1;
            }
        }
    }
    return 1;
}
int main()
{
    int a, b;
    double r, c;
    while(~scanf("%d%d%d%lf",&n,&m,&s,&val))//n为目的地
    {
        k = 0;
        init();
        for(int i = 1 ; i <= m ; i++ )
        {
            scanf("%d%d",&a,&b);
            scanf("%lf%lf",&r,&c);
            Addedge(a, b, r, c);//双向链表
            scanf("%lf%lf",&r,&c);
            Addedge(b, a, r, c);//双向链表
        }
        if(SPFA(s) == -1)
        {
            printf("YES\n");
        }
        else
            printf("NO\n");
    }
    return 0;
}

POJ 1860 & ZOJ 1544 Currency Exchange（最短路SPFA）

标签：poj   zju   最短路   spfa   

原文地址：http://blog.csdn.net/u012860063/article/details/39738181