hdu 3416 Marriage Match IV 最大流 最短路径

#include <cstdio>
#include <vector>
#include <queue>
#include <cstring>
using namespace std;
#define maxn 2100
#define INF 100000
struct node
{
int u,v,dis;
};
struct Edge
{
int from, to, cap, flow;
};

int n, m, s, t;
vector <node> map[maxn];
vector<Edge> edges;    // 边数的两倍
vector<int> G[maxn];   // 邻接表，G[i][j]表示结点i的第j条边在e数组中的序号
bool vis[maxn];        // BFS使用
int d[maxn];           // 从起点到i的距离
int cur[maxn];         // 当前弧指针
int dist[maxn];
int min(int a,int b)
{
if(a<b) return a;
else return b;
}
void AddEdge(int from, int to, int cap)
{
int len;
Edge temp;
temp.from=from;temp.to=to;temp.cap=cap;temp.flow=0;
edges.push_back(temp);
temp.from=to;temp.to=from;temp.cap=0;temp.flow=0;
edges.push_back(temp);
len = edges.size();
G[from].push_back(len-2);
G[to].push_back(len-1);
}
bool BFS()
{
memset(vis, 0, sizeof(vis));
queue<int> Q;
Q.push(s);
vis[s] = 1;
d[s] = 0;
while(!Q.empty())
{
int x = Q.front(); Q.pop();
for(int i = 0; i < G[x].size(); i++)
{
Edge& e = edges[G[x][i]];
if(!vis[e.to] && e.cap > e.flow)
{
vis[e.to] = 1;
d[e.to] = d[x] + 1;
Q.push(e.to);
}
}
}
return vis[t];
}
int DFS(int x, int a)
{
if(x == t || a == 0) return a;
int flow = 0, f;
for(int& i = cur[x]; i < G[x].size(); i++)
{
Edge& e = edges[G[x][i]];
if(d[x] + 1 == d[e.to] && (f = DFS(e.to, min(a, e.cap-e.flow))) > 0)
{
e.flow += f;
edges[G[x][i]^1].flow -= f;
flow += f;
a -= f;
if(a == 0) break;
}
}
return flow;
}
int Maxflow()
{
int flow = 0;
while(BFS())
{
memset(cur, 0, sizeof(cur));
flow += DFS(s, INF);
}
return flow;
}
void spfa()
{
int i,v,u;
memset(vis,0,sizeof(vis));
for(i=1;i<=n;i++)
dist[i]=INF;
queue<int> Q;
dist[s]=0;
Q.push(s);
while(!Q.empty())
{
u=Q.front();
Q.pop();
vis[u]=0;
for(i=0;i<map[u].size();i++)
{
v=map[u][i].v;
if(dist[v]>dist[u]+map[u][i].dis)
{
dist[v]=dist[u]+map[u][i].dis;
if(!vis[v])
{
vis[v]=1;
Q.push(v);
}
}
}
}
}

int main()
{
int cas;
scanf("%d",&cas);
while(cas--)
{
node temp;
int i,j,x,y,z;
scanf("%d%d",&n,&m);
for(i=0;i<=n+5;i++)
{
map[i].clear();
G[i].clear();
}
for(i=1;i<=m;i++)
{
scanf("%d%d%d",&x,&y,&z);
if(x==y)
continue;
temp.u=x;
temp.v=y;
temp.dis=z;
map[x].push_back(temp);
}
scanf("%d%d",&s,&t);
spfa();
for(i=1;i<=n;i++)
{
for(j=0;j<map[i].size();j++)
{
if(dist[i]+map[i][j].dis==dist[map[i][j].v])
AddEdge(i,map[i][j].v,1);
}
}
int ans=Maxflow();
printf("%d\n",ans);
}
return 0;
}