pku1860 Currency Exchange

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

图论，SPFA

好题

#include <stdio.h>
#include <string.h>
#include <queue>
#define N 1000100

using namespace std;

int n, m, src;
int x[N], y[N], len[N];
float dist[N];
bool inQue[N];
queue<int> que;
const int inf = 1<<30;
vector<pair<int, pair<float, float> > > g[N];
int count[N];
float src0;

int spfa()
{
    int i;
    for(i=0; i<N; i++)
    {
        inQue[i] = false;
        dist[i] = 0;
        count[i] = 0;
    }
    dist[src] = src0;
    while(!que.empty())
    {
        que.pop();
    }
    que.push(src);
    count[src] ++;
    inQue[src] = true;
    while(!que.empty())
    {
        int u = que.front();
        que.pop();
        for(i=0; i<g[u].size(); i++)
        {
            if((dist[u]-g[u][i].second.second)*g[u][i].second.first > dist[g[u][i].first])
            {
                dist[g[u][i].first] = (dist[u]-g[u][i].second.second)*g[u][i].second.first;
                if(!inQue[g[u][i].first])
                {
                    inQue[g[u][i].first] = true;
                    que.push(g[u][i].first);
                    count[g[u][i].first] ++;
                    if(count[g[u][i].first] > n)
                    {
                        return -1;
                    }
                }
            }
        }
        inQue[u] = false;
    }
    return 0;
}


int main()
{
    int x, y, t, i, j;
    float x1, x2, y1, y2;
    scanf("%d%d%d%f", &n, &m, &src, &src0);
    for(i=1; i<=m; i++)
    {
        scanf("%d%d%f%f%f%f", &x, &y, &x1, &x2, &y1, &y2);
        g[x].push_back(make_pair(y, make_pair(x1, x2)));
        g[y].push_back(make_pair(x, make_pair(y1, y2)));
    }
    if(spfa() == -1)
    {
        printf("YES\n");
    }
    else
    {
        printf("NO\n");
    }
    return 0;
}