[USACO4.2]Drainage Ditches

 1 #include<queue>
 2 #include<cstdio>
 3 #include<cctype>
 4 #include<vector>
 5 #include<cstring>
 6 inline int getint() {
 7     char ch;
 8     while(!isdigit(ch=getchar()));
 9     int x=ch^‘0‘;
10     while(isdigit(ch=getchar())) x=(((x<<2)+x)<<1)+(ch^‘0‘);
11     return x;
12 }
13 const int E=402,V=201,inf=0x7fffffff;
14 int s,t;
15 struct Edge {
16     int from,to,remain;
17 };
18 Edge e[E];
19 std::vector<int> g[V];
20 int sz=0;
21 inline void add_edge(const int u,const int v,const int w) {
22     e[sz]=(Edge){u,v,w};
23     g[u].push_back(sz);
24     sz++;
25 }
26 int a[V],p[V];
27 inline int Augment() {
28     memset(a,0,sizeof a);
29     a[s]=inf;
30     std::queue<int> q;
31     q.push(s);
32     while(!q.empty()&&!a[t]) {
33         int x=q.front();
34         q.pop();
35         for(unsigned i=0;i<g[x].size();i++) {
36             Edge &y=e[g[x][i]];
37             if(!a[y.to]&&y.remain) {
38                 p[y.to]=g[x][i];
39                 a[y.to]=std::min(a[x],y.remain);
40                 q.push(y.to);
41             }
42         }
43     }
44     return a[t];
45 }
46 inline int EdmondsKarp() {
47     int maxflow=0;
48     while(int flow=Augment()) {
49         for(int i=t;i!=s;i=e[p[i]].from) {
50             e[p[i]].remain-=flow;
51             e[p[i]^1].remain+=flow;
52         }
53         maxflow+=flow;
54     }
55     return maxflow;
56 }
57 int main() {
58     int n=getint(),m=getint();
59     s=1,t=m;
60     for(int i=0;i<n;i++) {
61         int u=getint(),v=getint(),w=getint();
62         add_edge(u,v,w);
63         add_edge(v,u,0);
64     }
65     printf("%d\n",EdmondsKarp());
66     return 0;
67 }