求help 这个数组表示的是什么意思
这是大牛的代码 谁能告诉我那个head有什么作用
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstring>
#define nMAX 1005
#define mMAX 210000
#define infl (long long)999999999*300
#define inf 1200
using namespace std;
int head[nMAX],has[nMAX],contain[nMAX],level[nMAX],qu[nMAX]; //head数组用来干什么的
long long map[nMAX][nMAX],high,low,mid;
int n,s_edge,s,t;
struct Edge
{
int u,v,cap,nxt;
}edge[mMAX];
long long maxl(long long a,long long b)
{
return a>b?a:b;
}
long long minl(long long a,long long b)
{
return a<b?a:b;
}
int min(int a,int b)
{
return a<b?a:b;
}
void floyd()
{
int i,j,k;
for(k=1;k<=n;k++)
for(i=1;i<=n;i++)
for(j=1;j<=n;j++)
{
if(map[i][k]==infl||map[k][j]==infl)continue;
map[i][j]=minl(map[i][j],map[i][k]+map[k][j]);
high=maxl(high,map[i][j]);
}
}
void addedge(int u,int v,int cap)
{
s_edge++;
edge[s_edge].v=v;
edge[s_edge].cap=cap;
edge[s_edge].nxt=head[u];
head[u]=s_edge; //这里的head
s_edge++;
edge[s_edge].v=u;
edge[s_edge].cap=0;
edge[s_edge].nxt=head[v];
head[v]=s_edge;
}
int dfs(int x,int cap)
{
if(x==t)return cap;
int temp=cap;
for(int e=head[x];e;e=edge[e].nxt)
{
int v=edge[e].v;
if(level[v]==level[x]+1&&temp>0&&edge[e].cap>0)
{
int tt=dfs(v,min(temp,edge[e].cap));
edge[e].cap-=tt;
edge[e^1].cap+=tt;
temp-=tt;
}
}
return cap-temp;
}
bool bfs()
{
int beg,tail;
for(int i=0;i<=t;i++)level[i]=-1;
//memset(level,-1,sizeof(level));
beg=0,tail=1;
qu[0]=0;
level[0]=0;
while(beg!=tail)
{
int u=qu[beg++];
for(int e=head[u];e;e=edge[e].nxt) //这里的head
{
int v=edge[e].v;
if(level[v]==-1&&edge[e].cap>0)
{
level[v]=level[u]+1;
qu[tail++]=v;
if(tail==nMAX)tail=0;
}
}
if(beg==nMAX)beg=0;
}
if(level[t]==-1)return 0;
return 1;
}
int dinic()
{
int SUM=0;
while(bfs())
{
SUM+=dfs(0,inf);
}
return SUM;
}
int main()
{
int x,y,i,j,p,num;
long long w;
while(~scanf("%d%d",&n,&p))
{
num=0;
for(i=1;i<=n;i++)
{
scanf("%d%d",&has[i],&contain[i]);
num+=has[i];
}
for(i=1;i<=n;i++)
for(j=1;j<=n;j++)
{
if(i==j)map[i][j]=0;
else map[i][j]=infl;
}
while(p--)
{
scanf("%d%d%lld",&x,&y,&w);
map[y][x]=map[x][y]=minl(map[x][y],w);
}
low=0,high=0;
floyd();
long long tt=++high;
while(high>low)
{
mid=(high+low)/2;
memset(head,0,sizeof(head));
s_edge=1;
s=0,t=2*n+1;
for(i=1;i<=n;i++)
{
addedge(s,i,has[i]);
addedge(i+n,t,contain[i]);
}
for(i=1;i<=n;i++)
for(j=1;j<=n;j++)
{
if(map[i][j]<=mid&&contain[j]>0)
{
addedge(i,j+n,inf);
}
}
int a=dinic();
if(a>=num)
{
high=mid;
}
else low=mid+1;
}
if(low==tt)printf("-1\n");
else printf("%lld\n",high);
}
return 0;
}
