"24 network flow problem" pilot program pairing problems

Question

Where have

Solution

Hungary bare title, but Iseek death Hit the network flow.

Code

#include<cstdio>
#include<algorithm>
#define N 10010
using namespace std;
struct node{int v,fr,c;}e[N<<3];
int n,m,x,y,tail[N<<1],S=0,T,cnt=1,ans=0;
int dis[N<<1],gap[N<<1];

inline int read()
{
    int x=0,f=0; char c=getchar();
    while (c<'0' || c>'9') f=(c=='-') ? 1:f,c=getchar();
    while (c>='0' && c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return f ? -x:x;
}

inline void add(int u,int v)
{
    e[++cnt]=(node){v,tail[u],1}; tail[u]=cnt;
    e[++cnt]=(node){u,tail[v],0}; tail[v]=cnt;
}

int dfs(int x,int hav)
{
    if (x==T) return hav;
    int gone=0;
    for (int p=tail[x],v,can;p;p=e[p].fr)
    {
        v=e[p].v;
        if (dis[x]!=dis[v]+1) continue;
        can=dfs(v,min(e[p].c,hav-gone));
        e[p].c-=can;e[p^1].c+=can;gone+=can;
        if (gone==hav) return gone;
    }
    gap[dis[x]]--;
    if (!gap[dis[x]]) dis[1]=T;
    gap[++dis[x]]++;
    return gone;
}

int main()
{
    freopen("air.in","r",stdin);
    freopen("air.out","w",stdout);
    n=read(),m=read();T=m+1;
    x=read(),y=read();
    while (x!=-1) add(x,y),x=read(),y=read();
    for (int i=1;i<=n;i++) add(S,i);
    for (int i=n+1;i<=m;i++) add(i,T);
    while (dis[1]!=T) ans+=dfs(S,1000000);
    if (ans==0) {puts("No Solution!"); return 0;}
    printf("%d\n",ans);
    for (int i=1;i<=n;i++)
        for (int p=tail[i];p;p=e[p].fr)
            if (e[p].v>=n+1 && e[p].v<=m && e[p].c==0)
                {printf("%d %d\n",i,e[p].v); break;}
    return 0;
}