HDU -- 4280 Island Transport（最大流）

#include<cstdio>
#include<cstring>
#include<iostream>
#include<queue>
#pragma comment(linker, "/STACK:1024000000,1024000000")
#define Min(a,b) ((a)<(b)?(a):(b))
#define Max(a,b) ((a)>(b)?(a):(b))
using namespace std;
const int N=100010;
const int INF=0x3f3f3f3f;
int head
,dis
,pre
,gap
,cur
,low
,s,t,n,m,top;

struct Edge{
int to,flow,next;
}edge[N*4];

void Addedge(int from,int to,int val){
edge[top].to=to,edge[top].flow=val,edge[top].next=head[from],head[from]=top++;
edge[top].to=from,edge[top].flow=0,edge[top].next=head[to],head[to]=top++;
}

void Bfs(){
queue<int> q;
memset(gap,0,sizeof(gap));
memset(dis,-1,sizeof(dis));
gap[0]=1;
dis[t]=0;
q.push(t);
while(!q.empty()){
int u=q.front();
q.pop();
for(int i=head[u];i+1;i=edge[i].next){
if(dis[edge[i].to]==-1&&edge[i].flow){
dis[edge[i].to]=dis[u]+1;
gap[dis[edge[i].to]]++;
q.push(edge[i].to);
}
}
}
}

int Sap(){
Bfs();
memset(pre,-1,sizeof(pre));
for(int i=1;i<=n;++i) cur[i]=head[i];
int u=s,i,cur_flow,max_flow=0,neck,tmp;
while(dis[s]<n){
if(u==t){
cur_flow=INF;
for(int i=s;i!=t;i=edge[cur[i]].to){
if(cur_flow>edge[cur[i]].flow){
neck=i;
cur_flow=edge[cur[i]].flow;
}
}
for(int i=s;i!=t;i=edge[cur[i]].to){
tmp=cur[i];
edge[tmp].flow-=cur_flow;
edge[tmp^1].flow+=cur_flow;
}
max_flow+=cur_flow;
u=neck;
}
int i;
for(i=cur[u];i!=-1;i=edge[i].next)
if(edge[i].flow&&dis[u]==dis[edge[i].to]+1) break;
if(i!=-1){
cur[u]=i;
pre[edge[i].to]=u;
u=edge[i].to;
}else{
if(--gap[dis[u]]==0) break;
cur[u]=head[u];
int mindis=n;
for(i=head[u];i!=-1;i=edge[i].next){
if(edge[i].flow&&mindis>dis[edge[i].to])
mindis=dis[edge[i].to];
}
dis[u]=mindis+1;
gap[dis[u]]++;
if(u!=s) u=pre[u];
}
}
return max_flow;
}

int main(){
int T;
scanf("%d",&T);
while(T--){
int u,v,val,x,y;
memset(head,-1,sizeof(head));
top=0;
scanf("%d%d",&n,&m);
int ss=INF,tt=0;
for(int i=1;i<=n;++i){
scanf("%d%d",&x,&y);
if(ss>x) ss=x,s=i;
if(tt<x) tt=x,t=i;
}
for(int i=0;i<m;++i){
scanf("%d%d%d",&u,&v,&val);
Addedge(u,v,val);
Addedge(v,u,val);
}
int res=0;
res=Sap();
printf("%d\n",res);
}
}