UVA 1658 Admiral——拆点法+最小费最大流

对于边u->v的处理方法是先建立边u->u+n，权值为0， 然后建立边u+n->v权值为c，这样可以避免一个点经过多次的情况

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <vector>#include <queue>using namespace std;const int INF = 0x3f3f3f3f;const int maxn = 2 * 1e3 + 10;struct Edge {    int from, to, cap, flow, cost;    Edge (int u, int v, int c, int f, int w) : from(u), to(v), cap(c), flow(f), cost(w) {}};struct MCMF {    int n, m;    vector<Edge> edges;    vector<int> G[maxn];    int inq[maxn], d[maxn], p[maxn], a[maxn];    void init(int x) {        n = x;        edges.clear();        for (int i = 0; i <= n; i++) G[i].clear();    }    void addedge(int from, int to, int cap, int cost) {        edges.push_back(Edge(from, to, cap, 0, cost));        edges.push_back(Edge(to, from, 0, 0, -cost));        m = edges.size();        G[from].push_back(m - 2);        G[to].push_back(m - 1);    }    bool BellmanFord(int s, int t, int &flow, long long &cost) {        memset(inq, 0, sizeof(inq));        for (int i = 0; i <= n; i++) d[i] = INF;        inq[s] = 1, d[s] = 0, p[s] = 0, a[s] = INF;        queue<int> q; q.push(s);        while (!q.empty()) {            int u = q.front(); q.pop();            inq[u] = 0;            for (int i = 0; i < G[u].size(); i++) {                Edge &e = edges[G[u][i]];                if (e.cap > e.flow && d[e.to] > d[u] + e.cost) {                    d[e.to] = d[u] + e.cost;                    p[e.to] = G[u][i];                    a[e.to] = min(a[u], e.cap - e.flow);                    if (!inq[e.to]) { q.push(e.to); inq[e.to] = 1; }                }            }        }        if (d[t] == INF) return false;        flow += a[t];        cost += (long long)d[t] * (long long)a[t];        for (int u = t; u != s; u = edges[p[u]].from) {            edges[p[u]].flow += a[t];            edges[p[u]^1].flow -= a[t];        }        return true;    }    int mincostmaxflow(int s, int t, long long &cost) {        int flow = 0; cost = 0;        while (BellmanFord(s, t, flow, cost));        return flow;    }};int main() {    MCMF mcmf;    int n, m;    while (~scanf("%d %d", &n, &m)) {        mcmf.init(n<<1);        for (int i = 2; i <= n - 1; i++) mcmf.addedge(i, i + n, 1, 0);        mcmf.addedge(1, n + 1, 2, 0);        mcmf.addedge(n, n<<1, 2, 0);        for (int i = 0; i < m; i++) {            int u, v, cost; scanf("%d %d %d", &u, &v, &cost);            mcmf.addedge(u + n, v, 1, cost);        }        long long cost = 0;        mcmf.mincostmaxflow(1, n<<1, cost);        cout << cost << endl;    }    return 0;}