Optimal Bus Route Design UVA 1349

将每个点分成两个点，然后再来建立相应的有向边，转换为最小完美匹配问题，按照最小费用最大流问题来求解即可，具体实现见如下代码:

#include<iostream>#include<vector>#include<string>#include<set>#include<stack>#include<queue>#include<map>#include<algorithm>#include<cmath>#include<iomanip>#include<cstring>#include<sstream>#include<cstdio>#include<deque>#include<functional>using namespace std;class Edge{public:int from, to, cap, flow, cost;Edge(int fr, int t, int ca, int fl, int c):from(fr),to(t),cap(ca),flow(fl),cost(c){}};class Solve{public:int n;vector<Edge> edge;vector<int> G[210];const int Inf = 0x3f3f3f3f;void addEgde(int from,int to,int cap,int flow,int cost){edge.push_back(Edge(from,to,cap,flow,cost));edge.push_back(Edge(to,from,0,0,-cost));int m = edge.size();G[from].push_back(m-2);G[to].push_back(m - 1);}void Init(){edge.clear();for (int i = 0; i < 210; i++) G[i].clear();for (int i = 1; i <= n; i++){addEgde(0,i,1,0,0);addEgde(n + i, 2 * n + 1, 1, 0, 0);}for (int i = 1; i <= n; i++){while (true){int a, b;cin >> a;if (a == 0) break;cin >> b;addEgde(i, a + n, 1, 0, b);}}}bool BellmanFloyd(int start,int end,int &flow,int &cost){int price[210];memset(price, Inf, sizeof(price));price[start] = 0;int parent[210];int Flow[210],inq[210];Flow[start] = Inf;memset(inq, 0, sizeof(inq));queue<int> q;q.push(start);inq[start] = 1;while (!q.empty()){int id = q.front();q.pop();inq[id] = 0;for (int i = 0; i < G[id].size(); i++){int ide = G[id][i];int to = edge[ide].to;if (edge[ide].cap > edge[ide].flow&&price[to] > price[id] + edge[ide].cost){Flow[to] = min(Flow[id], edge[ide].cap - edge[ide].flow);price[to] = price[id] + edge[ide].cost;parent[to] = ide;if (!inq[to]){q.push(to);inq[to] = 1;}}}}if (price[end] == Inf) return false;flow += Flow[end];cost += price[end] * Flow[end];for (int i = end; i != start; i = edge[parent[i]].from){edge[parent[i]].flow += Flow[end];edge[parent[i] ^ 1].flow -= Flow[end];}return true;}void MaxFlow(int start,int end){int flow = 0, cost = 0;while (BellmanFloyd(start, end, flow, cost));if (flow < n) cout << "N" << endl;else cout << cost << endl;}void Deal(){Init();MaxFlow(0, 2 * n + 1);}};int main(){Solve a;while (cin >> a.n){if (a.n == 0) break;a.Deal();}return 0;}