hdu Flow Problem （最大流 裸题）

view code#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
using namespace std;
const int INF = 0x3f3f3f3f;
const int maxn = 1000;
int n, m, s, t, cas=1, _;
int pre[maxn], d[maxn], cur[maxn];
bool vis[maxn];

struct Edge
{
int from, to, cap, flow, p;
Edge() {}
Edge(int from, int to, int cap, int flow, int pre):from(from), to(to), cap(cap), flow(flow), p(pre) {}
}e[maxn*maxn];
int ecnt = 0;

void init()
{
memset(pre, -1, sizeof(pre));
ecnt = 0;
s = 1, t = n;
}

bool BFS()
{
memset(vis, 0, sizeof(vis));
queue<int > q;
q.push(s);
vis[s] = 1; d[s] = 0;
while(!q.empty())
{
int u = q.front(); q.pop();
for(int i = pre[u]; ~i; i=e[i].p)
{
int v = e[i].to;
if(!vis[v] && e[i].flow<e[i].cap)
{
d[v] = d[u] + 1;
vis[v] = true;
q.push(v);
}
}
}
return vis[t];
}

int DFS(int u, int c)
{
if(u==t || c==0) return c;
int flow = 0, f;
for(int &i=cur[u]; ~i; i=e[i].p)
{
int v = e[i].to;
if(d[v]==d[u]+1 && (f=DFS(v, min(c, e[i].cap-e[i].flow)))>0)
{
e[i].flow += f;
e[i^1].flow -= f;
flow += f;
c -= f;
if(c==0) break;
}
}
return flow;
}

int main()
{
//    freopen("in.txt", "r", stdin);
scanf("%d", &_);
while(_--)
{
scanf("%d%d", &n, &m);
init();
int  u, v, w;
for(int i=0; i<m; i++)
{
scanf("%d%d%d", &u, &v, &w);
e[ecnt] = Edge(u, v, w, 0, pre[u]);
pre[u] = ecnt++;
e[ecnt] = Edge(v, u, 0, 0, pre[v]);
pre[v] = ecnt++;
}
int ans = 0;
while(BFS())
{
for(int i=1; i<=n; i++) cur[i] = pre[i];
ans += DFS(s, INF);
}
printf("Case %d: %d\n", cas++, ans);
}
}