BZOJ 3931 [CQOI2015]网络吞吐量

【在期末考试复习的间隙做题真的很不容易啊qaq

【下周就要期末考试了，祝我能考个好成绩ovo

 

sb题，先跑一遍最短路预处理，然后按照题目加边跑最大流就没了。注意答案要用long long存储。

跟BZOJ 1266有点像呀。

注意结点容量的处理方法：对于每个点s，设它的结点容量为c。把s拆成两个点s1和s2，从s1往s2连一条容量为c的边；对于终点为s的边，其终点为s1；对于起点为s的边，其起点为s2。

 

  1 #include <queue>
  2 #include <cstdio>
  3 #include <cstring>
  4 
  5 using namespace std;
  6 
  7 const size_t Max_N(1050);
  8 const size_t Max_M(600050);
  9 const long long int INF(0X7F7F7F7F7F7F7F7FLL);
 10 
 11 void Get_Val(int &Ret)
 12 {
 13     Ret = 0;
 14     char ch;
 15     while ((ch = getchar()), (ch > '9' || ch < '0'))
 16         ;
 17     do
 18     {
 19         (Ret *= 10) += ch - '0';
 20     }
 21     while ((ch = getchar()), (ch >= '0' && ch <= '9'));
 22 }
 23 
 24 int N;
 25 int G[Max_N][Max_N];
 26 
 27 int total;
 28 int head[Max_N];
 29 int to[Max_M], next[Max_M], weight[Max_M];
 30 
 31 void add_edge(const int &s, const int &t, const int &w)
 32 {
 33     ++total;
 34     to[total] = t, weight[total] = w;
 35     next[total] = head[s], head[s] = total;
 36 }
 37 
 38 struct Flow_Graph
 39 {
 40     Flow_Graph() : V(0), Total(0) 
 41     {
 42         memset(Head, 0, sizeof(Head));
 43         memset(To, 0, sizeof(To)), memset(Next, 0, sizeof(Next));
 44         memset(Cap, 0, sizeof(Cap)), memset(Flow, 0, sizeof(Flow));
 45     }
 46     int V;
 47     int Total;
 48     int Head[Max_N], Cur[Max_N];
 49     int To[Max_M], Next[Max_M];
 50     long long int Cap[Max_M], Flow[Max_M];
 51     int Dist[Max_N];
 52     int S, T;
 53     
 54     inline
 55     void Add_Edge(const int &tot, const int &s, const int &t, const long long int &c)
 56     {
 57         To[tot] = t;
 58         Next[tot] = Head[s], Head[s] = tot;
 59         Cap[tot] = c, Flow[tot] = 0;
 60     }
 61     inline
 62     void Add_Link(const int &s, const int &t, const long long int &c)
 63     {
 64         Total += 2;
 65         Add_Edge(Total, s, t, c);
 66         Add_Edge(Total ^ 1, t, s, 0);
 67     }
 68     
 69     bool BFS();
 70     long long int DFS(const int&, long long int);
 71     long long int Dinic();
 72 };
 73 Flow_Graph MFG;
 74 
 75 void init()
 76 {
 77     int M, a, b, d;
 78     Get_Val(N), Get_Val(M);
 79     memset(G, 0X3F, sizeof(G));
 80     for (int i = 1;i <= N;++i)
 81         G[i][i] = 0;
 82     while (M--)
 83     {
 84         Get_Val(a), Get_Val(b), Get_Val(d);
 85         G[a][b] = G[b][a] = min(G[a][b], d);
 86         add_edge(a, b, d), add_edge(b, a, d);
 87     }
 88 }
 89 
 90 void Floyd()
 91 {
 92     for (int k = 1;k <= N;++k)
 93         for (int i = 1;i <= N;++i)
 94             for (int j = 1;j <= N;++j)
 95                 G[i][j] = min(G[i][j], G[i][k] + G[k][j]);
 96 }
 97 
 98 void make_graph()
 99 {
100     Floyd();
101     int s, t, c;
102     MFG.V = (N << 1), MFG.S = 1, MFG.T = (N << 1);
103     for (s = 1;s <= N;++s)
104         for (int i = head[s];i;i = next[i])
105         {
106             t = to[i];
107             if (G[1][N] == G[1][s] + weight[i] + G[t][N])
108                 MFG.Add_Link(s + N, t, INF);
109         }
110     for (int i = 1;i <= N;++i)
111     {
112         Get_Val(c);
113         if (i != 1 && i != N)
114             MFG.Add_Link(i, i + N, c);
115         else
116             MFG.Add_Link(i, i + N, INF);
117     }
118 }
119 
120 bool Flow_Graph::BFS()
121 {
122     memset(Dist, 0, sizeof(Dist));
123     queue<int> Q;
124     Dist[S] = 1, Q.push(S);
125     int Top;
126     while (Q.size())
127     {
128         Top = Q.front(), Q.pop();
129         for (int i = Head[Top];i;i = Next[i])
130             if (!Dist[To[i]] && Cap[i] > Flow[i])
131             {
132                 Dist[To[i]] = Dist[Top] + 1;
133                 Q.push(To[i]);
134             }
135     }
136     return Dist[T];
137     
138 }
139 
140 long long int Flow_Graph::DFS(const int &u, long long int a)
141 {
142     if (u == T || a == 0LL)
143         return a;
144     long long int Ans(0LL), f;
145     for (int &i = Cur[u];i;i = Next[i])
146         if (Dist[To[i]] == Dist[u] + 1)
147             if ((f = DFS(To[i], min(a, Cap[i] - Flow[i]))) > 0)
148             {
149                 Flow[i] += f;
150                 Flow[i ^ 1] -= f;
151                 Ans += f;
152                 a -= f;
153                 if (a == 0LL)
154                     break;
155             }
156     return Ans;
157 }
158 
159 long long int Flow_Graph::Dinic()
160 {
161     long long int Ans(0LL);
162     while (BFS())
163     {
164         for (int i = 1;i <= V;++i)
165             Cur[i] = Head[i];
166         Ans += DFS(S, INF);
167     }
168     return Ans;
169 }
170 
171 int main()
172 {
173     init();
174     make_graph();
175     printf("%lld", MFG.Dinic());
176     return 0;
177 }

BZOJ 3931