Currency Exchange(POJ1860 判正环)

~题目链接~

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

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

1.Spfa

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<queue>
#define maxn 2<<28
#define maxm 1000+10

using namespace std;

struct node
{
    double x,y;
} map[maxm][maxm];

double dis[maxm];
queue<int>Q;

int Spfa(int n,int s,double k)
{
    while(!Q.empty())
        Q.pop();
    int flag[maxm],i;
    memset(flag,0,sizeof(flag));
    for(i=1; i<=n; i++)
        dis[i]=maxn;
    Q.push(s);
    dis[s]=k;
    flag[s]=1;
    while(!Q.empty())
    {
        int h=Q.front();
        Q.pop();
        flag[h]=0;
        for(i=1; i<=n; i++)
            if(dis[i]<(dis[h]-map[h][i].y)*map[h][i].x)//松弛
            {
                dis[i]=(dis[h]-map[h][i].y)*map[h][i].x;
                if(!flag[i])
                {
                    Q.push(i);
                    flag[i]=1;
                }
            }
        if(dis[s]>k)//判断是否存在正环
            return 1;
    }
    return 0;
}

int main()
{
    int n,m,s,a,b,i;
    double k,u,v,w,z;
    while(~scanf("%d%d%d%lf",&n,&m,&s,&k))
    {
        for(i=0; i<m; i++)
        {
            scanf("%d%d%lf%lf%lf%lf",&a,&b,&u,&v,&w,&z);
            map[a][b].x=u;
            map[a][b].y=v;
            map[b][a].x=w;
            map[b][a].y=z;
        }
        if(Spfa(n,s,k))
            printf("YES
");
        else
            printf("NO
");
    }
    return 0;
}

2.Bellman_ford

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define maxm 1000+10

struct node
{
    int u,v;
    double x,y;
} map[maxm];

double dis[maxm];
int num;

int Bellman_ford(int n,int s,double k)
{
    int i,j,flag;
    memset(dis,0,sizeof(dis));
    dis[s]=k;
    for(i=0; i<n; i++)
    {
        flag=0;
        for(j=1; j<=num; j++)
            if(dis[map[j].v]<(dis[map[j].u]-map[j].y)*map[j].x)
            {
                dis[map[j].v]=(dis[map[j].u]-map[j].y)*map[j].x;
                flag=1;
            }
        if(!flag)
            break;
    }
    if(i>=n)//判断松弛后，是否存在正环
        return 1;
    return 0;
}

int main()
{
    int n,m,s,a,b,i;
    double k,u,v,w,z;
    while(~scanf("%d%d%d%lf",&n,&m,&s,&k))
    {
        num=0;
        for(i=0; i<m; i++)
        {
            scanf("%d%d%lf%lf%lf%lf",&a,&b,&u,&v,&w,&z);
            map[++num]=((struct node){a,b,u,v});
            map[++num]=((struct node){b,a,w,z});
        }
        if(Bellman_ford(n,s,k))
            printf("YES
");
        else
            printf("NO
");
    }
    return 0;
}