POJ2240_SPFA判断负环,Floyd也可以做(计算最大汇率,当自己到自己的最大汇率大于1时成立)

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//因为vector的P[]没有clear所以疯狂wa#include<iostream>#include<algorithm>#include<queue>#include<cstring>#include<vector>#include<string>#include<map>#include<cstdio>#define Max 0x3f3f3f3fusing namespace std;map<string, int> M;const int maxn = 50;double Map[maxn][maxn];int cnt[maxn];bool vis[maxn];bool book[maxn];vector<int> P[maxn];double D[maxn];bool boo[maxn][maxn];int Du[maxn];bool spfa(int id, int n)//找与id节点相连接的负环{    queue<int> Q;    memset(D, 0, sizeof(D));    D[id] = 1.0;    memset(cnt, 0, sizeof(cnt));    memset(vis, 0, sizeof(vis));    Q.push(id);    vis[id] = 1;    book[id] = 1;    cnt[id]++;    while (!Q.empty())    {        int u = Q.front();        Q.pop();        vis[u] = false;        for (int i = 0; i < P[u].size(); i++)        {            int v = P[u][i];//u的终结点            if (!book[v])            {                book[v] = 1;            }            double tt = D[u]*Map[u][v];            if (tt > D[v])            {                D[v] = tt;                if (!vis[v])                {                    vis[v] = true;                    Q.push(v);                    cnt[v]++;                    if (cnt[v] > Du[v])//其实只要大于这个点的入度就行                        return true;                }            }        }    }    return false;}int main(){    int n;    int cas = 1;    while (~scanf("%d", &n) && n)    {        memset(Du, 0, sizeof(Du));        cout << "Case " << cas++ << ": ";        string s;        M.clear();        int c = 1;        for (int i = 0; i < n; i++)        {            cin >> s;            P[i].clear();            if (M[s] == 0)            {                M[s] = c++;            }        }        n = c - 1;        int m;        cin >> m;        for (int i = 0; i < n; i++)        {            for (int j = 0; j < n; j++)            {                Map[i][j] = 0;            }        }        string s0, s1;        double r;        memset(boo, 0, sizeof(boo));        for (int i = 0; i < m; i++)        {            cin >> s0 >> r >> s1;            int x = M[s0]-1;            int y = M[s1]-1;            Map[x][y] = r;            boo[x][y] = 1;        }        for (int i = 0; i < n; i++)        {            for (int j = 0; j <n ; j++)            {                if (boo[i][j])                {                    P[i].push_back(j);                    Du[j]++;                }            }        }        memset(book, 0, sizeof(book));        bool ans = false;        for (int i = 0; i < n; i++)        {            if (!book[i])//这一步是一处优化            {                if (spfa(i, n))                {                    ans = true;                    break;                }            }        }        if (ans)        {            cout << "Yes" << endl;        }        else        {            cout << "No" << endl;        }    }    return 0;}
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