Drainage Ditches---hdu1532（最大流, 模板）

#include<stdio.h>
#include<string.h>
#include<queue>
#include<algorithm>
using namespace std;

#define N 220
#define INF 0xfffffff

int n, ans, Head
, cnt, Layer
;
struct Edge
{
int v, flow, next;
} e[2*N];

void Add(int u, int v, int flow)
{
e[cnt].v = v;
e[cnt].flow = flow;
e[cnt].next = Head[u];
Head[u] = cnt++;
}
bool bfs(int S, int E)
{
memset(Layer, 0, sizeof(Layer));
Layer[S] = 1;
queue<int>Q;
Q.push(S);
int p, q;
while(!Q.empty())
{
p = Q.front();
Q.pop();
if(p == E)return true;
for(int i=Head[p]; i!=-1; i=e[i].next)
{
q = e[i].v;
if(!Layer[q] && e[i].flow)
{
Layer[q] = Layer[p]+1;
Q.push(q);
}
}
}
return false;
}
int dfs(int u, int MaxFlow, int E)
{
if(u == E)return MaxFlow;
int  uflow=0;
for(int i=Head[u]; i!=-1; i=e[i].next)
{
int v = e[i].v;
if(Layer[v]==Layer[u]+1 && e[i].flow)
{
int flow = min(e[i].flow, MaxFlow - uflow);
flow = dfs(v, flow, E);

e[i].flow -= flow;
e[i^1].flow += flow;
uflow += flow;
if(uflow==MaxFlow)break;
}
}
if(uflow==0)
Layer[u]=0;
return uflow;
}
void Dinic()
{
while(bfs(1, n))
{
ans+=dfs(1, INF, n);
}
}
int main()
{
int a, b, flow, m;
while(scanf("%d%d", &m, &n)!=EOF)
{
memset(Head, -1, sizeof(Head));
cnt = 0;
for(int i=1; i<=m; i++)
{
scanf("%d%d%d", &a, &b, &flow);
Add(a, b, flow);
Add(b, a, 0);
}
ans = 0;
Dinic();
printf("%d\n", ans);
}
return 0;
}