POJ 1860 Currency Exchange——spfa判正环

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dis初始化为0，dis[S] = V, 松弛操作为if (dis [u] < (dis[v] - c) * v) dis [u] = (dis[v] - c) * v,结束条件为dis[S] > V

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <vector>#include <queue>using namespace std;const int INF = 0x3f3f3f3f;const int maxn = 1010;bool vis[maxn];int N, M, S;double V, dis[maxn];struct Date {    int x;    double C, R;    Date(int xx, double cc, double rr) : x(xx), C(cc), R(rr) {}};vector<Date> G[maxn];bool spfa() {    for (int i = 1; i <= N; i++) dis[i] = 0, vis[i] = false;    dis[S] = V, vis[S] = true;    queue<int> q; q.push(S);    while (!q.empty()) {        int u = q.front(); q.pop();        vis[u] = false;        for (int i = 0; i < G[u].size(); i++) {            int v = G[u][i].x;            double c = G[u][i].C, r = G[u][i].R;            if (dis[v] < (dis[u] - c) * r) {                dis[v] = (dis[u] - c) * r;                if (!vis[v]) vis[v] = true, q.push(v);            }        }        if (dis[S] > V) return true;    }    return false;}int main() {    int u, v;    double C1, R1, C2, R2;    while (~scanf("%d %d %d %lf", &N, &M, &S, &V)) {        for (int i = 1; i <= N; i++) G[i].clear();        while (M--) {            scanf("%d %d %lf %lf %lf %lf", &u, &v, &R1, &C1, &R2, &C2);            G[u].push_back(Date(v, C1, R1));            G[v].push_back(Date(u, C2, R2));        }        if(spfa()) printf("YES\n");        else printf("NO\n");    }    return 0;}

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