poj3469 Dual Core CPU

Posted 2020-10-16 王宜鸣

思路：

最小割。

实现：

 1 #include <iostream>
 2 #include <vector>
 3 #include <cstring>
 4 #include <queue>
 5 using namespace std;
 6 
 7 const int MAXV = 20005, INF = 0x3f3f3f3f;
 8 struct edge
 9 {
10     int to, cap, rev;
11     edge(int t, int c, int r) { to = t; cap = c; rev = r; }
12 };
13 int level[MAXV];
14 int iter[MAXV];
15 vector<edge> G[MAXV];
16 void add_edge(int from, int to, int cap)
17 {
18     edge e(to, cap, G[to].size());
19     G[from].push_back(e);
20     edge er(from, 0, G[from].size() - 1);
21     G[to].push_back(er);
22 }
23 void bfs(int s)
24 {
25     memset(level, -1, sizeof level);
26     queue<int> q;
27     level[s] = 0;
28     q.push(s);
29     while (!q.empty())
30     {
31         int v = q.front(); q.pop();
32         for (int i = 0; i < G[v].size(); i++)
33         {
34             edge& e = G[v][i];
35             if (e.cap > 0 && level[e.to] < 0)
36             {
37                 level[e.to] = level[v] + 1;
38                 q.push(e.to);
39             }
40         }
41     }
42 }
43 int dfs(int v, int t, int f)
44 {
45     if (v == t) return f;
46     for (int& i = iter[v]; i < G[v].size(); i++)
47     {
48         edge& e = G[v][i];
49         if (e.cap > 0 && level[v] < level[e.to])
50         {
51             int d = dfs(e.to, t, min(f, e.cap));
52             if (d > 0)
53             {
54                 e.cap -= d;
55                 G[e.to][e.rev].cap += d;
56                 return d;
57             }
58         }
59     }
60     return 0;
61 }
62 int max_flow(int s, int t)
63 {
64     int flow = 0;
65     for (;;)
66     {
67         bfs(s);
68         if (level[t] < 0) return flow;
69         memset(iter, 0, sizeof iter);
70         int f = 0;
71         while ((f = dfs(s, t, INF)) > 0)
72             flow += f;
73     }
74 }
75 
76 int main()
77 {
78     ios::sync_with_stdio(false);
79     int n, m, x, y, w;
80     cin >> n >> m;
81     for (int i = 1; i <= n; i++)
82     {
83         cin >> x >> y;
84         add_edge(0, i, x);
85         add_edge(i, n + 1, y);
86     }
87     for (int i = 1; i <= m; i++)
88     {
89         cin >> x >> y >> w;
90         add_edge(x, y, w);
91         add_edge(y, x, w);
92     }
93     cout << max_flow(0, n + 1) << endl;
94     return 0;
95 }