hdu3549Flow Problem【最大流】
Flow Problem
Time Limit: 5000/5000 MS (Java/Others) Memory Limit: 65535/32768 K (Java/Others)
Total Submission(s): 6817 Accepted Submission(s): 3178
Problem Description
Network flow is a well-known difficult problem for ACMers. Given a graph, your task is to find out the maximum flow for the weighted directed graph.
Input
The first line of input contains an integer T, denoting the number of test cases.
For each test case, the first line contains two integers N and M, denoting the number of vertexes and edges in the graph. (2 <= N <= 15, 0 <= M <= 1000)
Next M lines, each line contains three integers X, Y and C, there is an edge from X to Y and the capacity of it is C. (1 <= X, Y <= N, 1 <= C <= 1000)
For each test case, the first line contains two integers N and M, denoting the number of vertexes and edges in the graph. (2 <= N <= 15, 0 <= M <= 1000)
Next M lines, each line contains three integers X, Y and C, there is an edge from X to Y and the capacity of it is C. (1 <= X, Y <= N, 1 <= C <= 1000)
Output
For each test cases, you should output the maximum flow from source 1 to sink N.
Sample Input
2
3 2
1 2 1
2 3 1
3 3
1 2 1
2 3 1
1 3 1
Sample Output
Case 1: 1
Case 2: 2
Author
HyperHexagon
Source
题意:最大流
分析:最大流模板
代码:
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <queue> 5 #include <vector> 6 using namespace std; 7 8 const int maxn = 20 << 1; 9 const int INF = 1000000000; 10 11 struct Edge 12 { 13 int from, to, cap, flow; 14 }; 15 16 struct Dinic 17 { 18 int n, m, s, t; 19 vector<Edge> edges; 20 vector<int>G[maxn]; 21 bool vis[maxn]; 22 int d[maxn]; 23 int cur[maxn]; 24 25 void ClearAll(int n) { 26 for(int i = 0; i <= n; i++) { 27 G[i].clear(); 28 } 29 edges.clear(); 30 } 31 32 void AddEdge(int from, int to, int cap) { 33 edges.push_back((Edge){from, to, cap, 0} ); 34 edges.push_back((Edge){to, from, 0, 0} ); 35 m = edges.size(); 36 G[from].push_back(m - 2); 37 G[to].push_back(m - 1); 38 //printf("%din end\n",m); 39 } 40 41 bool BFS() 42 { 43 memset(vis, 0, sizeof(vis) ); 44 queue<int> Q; 45 Q.push(s); 46 vis[s] = 1; 47 d[s] = 0; 48 while(!Q.empty() ){ 49 int x = Q.front(); Q.pop(); 50 for(int i = 0; i < G[x].size(); i++) { 51 Edge& e = edges[G[x][i]]; 52 if(!vis[e.to] && e.cap > e.flow) { 53 vis[e.to] = 1; 54 d[e.to] = d[x] + 1; 55 Q.push(e.to); 56 } 57 } 58 } 59 return vis[t]; 60 } 61 62 int DFS(int x, int a) { 63 if(x == t || a == 0) return a; 64 int flow = 0, f; 65 for(int& i = cur[x]; i < G[x].size(); i++) { 66 Edge& e = edges[G[x][i]]; 67 if(d[x] + 1 == d[e.to] && (f = DFS(e.to, min(a, e.cap - e.flow))) > 0) { 68 e.flow += f; 69 edges[G[x][i]^1].flow -= f; 70 flow += f; 71 a -= f; 72 if(a == 0) break; 73 } 74 } 75 return flow; 76 } 77 78 int Maxflow(int s, int t) { 79 this -> s = s; this -> t = t; 80 int flow = 0; 81 while(BFS()) { 82 memset(cur, 0, sizeof(cur) ); 83 flow += DFS(s, INF); 84 } 85 return flow; 86 } 87 }; 88 89 Dinic g; 90 91 int main() 92 { 93 int t; 94 scanf("%d",&t); 95 int n, m; 96 int a, b, c; 97 for(int kase = 1; kase <= t; kase++) { 98 scanf("%d %d",&n, &m); 99 g.ClearAll(maxn); 100 for(int i = 0;i < m; i++ ) { 101 scanf("%d %d %d",&a, &b, &c); 102 g.AddEdge(a, b, c); 103 } 104 printf("Case %d: %d\n",kase, g.Maxflow(1, n) ); 105 } 106 return 0; 107 }