COGS 11. 运输问题1

#include <cstdio>
#include <queue>
#define Max 1000
#define inf 1e9

using namespace std;

struct Edge
{
    int next,to,dis;
}edge[Max*Max*2];
int n,head[Max*Max*2],cnt=1,dep[Max*Max*2];
void add(int u,int v,int l)
{
    Edge*now=&edge[++cnt];
    now->next=head[u];
    now->to=v;
    now->dis=l;
    head[u]=cnt;
}
bool bfs(int s,int t)
{
    queue<int>q;
    q.push(s);
    for(int i=1;i<=n;++i) dep[i]=inf;
    dep[s]=0;
    while(!q.empty())
    {
        int tp=q.front();
        q.pop();
        for(int i=head[tp];i;i=edge[i].next)
        {
            int v=edge[i].to;
            if(dep[v]>dep[tp]+1&&edge[i].dis)
            {
                dep[v]=dep[tp]+1;
                if(v==t) return 1;
                q.push(v);
            }
        }
    }
    return 0;
}
int dfs(int now,int t,int came_flow)
{
    if(t==now||came_flow==0)
    return came_flow;
    int res=0,f;
    for(int i=head[now];i;i=edge[i].next)
    {
        int v=edge[i].to;
        if(dep[v]==dep[now]+1&&edge[i].dis&&(f=dfs(v,t,min(came_flow,edge[i].dis))))
        {
            res+=f;
            came_flow-=f;
            edge[i].dis-=f;
            edge[i^1].dis+=f;
            if(came_flow==0)
            break;
        }
    }
    return res;
} 
int dinic(int s,int t)
{
    int ans=0;
    while(bfs(s,t))
    ans+=dfs(s,t,inf);
    return ans;
}
int main()
{
    freopen("maxflowa.in","r",stdin);
    freopen("maxflowa.out","w",stdout);
    scanf("%d",&n);
    for(int a,i=1;i<=n;++i)
    {
        for(int j=1;j<=n;++j)
        {
            scanf("%d",&a);
            if(a)
            {
                add(i,j,a);
                add(j,i,0); 
            }
        }
    }
    printf("%d",dinic(1,n));
    return 0;
}