网络流24题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
#include <ctime>
#include <vector>
#include <queue>
#include <map>
#include <stack>
#include <set>
#include <bitset>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define ms(a, b) memset(a, b, sizeof(a))
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define IOS ios::sync_with_stdio(0);cin.tie(0);
#define random(a, b) rand()*rand()%(b-a+1)+a
#define pi acos(-1)
const ll INF = 0x3f3f3f3f3f3f3f3fll;
const int inf = 0x3f3f3f3f;
const int maxn = 1000 + 10;
const int maxm = 3000000 +10;
const int mod = 1000000000;

int maze[maxn][maxn];
int gap[maxn],dis[maxn],pre[maxn],cur[maxn];
int sap(int start,int ed,int nodenum){
    memset(cur,0,sizeof(cur));
    memset(dis,0,sizeof(dis));
    memset(gap,0,sizeof(gap));
    int u = pre[start]=start,maxflow=0,aug=-1;
    gap[0]=nodenum;
    while(dis[start]<nodenum){
        loop:
            for(int v =cur[u];v<nodenum;v++){
                if(maze[u][v]&&dis[u]==dis[v]+1){
                    if(aug==-1||aug>maze[u][v]) aug = maze[u][v];
                    pre[v]=u;
                    u=cur[u]=v;
                    if(v==ed){
                        maxflow+=aug;
                        for(u=pre[u];v!=start;v=u,u=pre[u]){
                            maze[u][v]-=aug;
                            maze[v][u]+=aug;
                        }
                        aug=-1;
                    }
                    goto loop;
                }
            }
            int mindis = nodenum-1;
            for(int v=0;v<nodenum;v++){
                if(maze[u][v]&&mindis>dis[v]){
                    cur[u]=v;
                    mindis=dis[v];
                }
            }
            if((--gap[dis[u]])==0) break;
            gap[dis[u]=mindis+1]++;
            u=pre[u];
    }
    return maxflow;
}

int main(){
#ifdef LOCAL
    freopen("in.txt","r",stdin);
#endif // LOCAL
    int n,m;
    while(~scanf("%d%d",&m,&n)){
        memset(maze,0,sizeof(maze));
        for(int i=1;i<=m;i++) maze[0][i]=1;
        for(int i=m+1;i<=n;i++) maze[i][n+1]=1;
        int x,y;
        while(true){
            scanf("%d%d",&x,&y);
            if(x==-1&&y==-1) break;
            maze[x][y]=1;
        }
        int ans=sap(0,n+1,n+2);
        cout<<ans<<endl;

        for(int i=1;i<=m;i++){
            for(int j=m+1;j<=n;j++){
                if(maze[i][j]==0&&maze[j][i]==1){
                    printf("%d %d\n",i,j);
                    break;
                }
            }
        }
    }
    return 0;
}