【网络流24题】火星探险问题

题面

https://www.luogu.org/problemnew/show/P3356

题解

拆点+费用流

alpq654321讲过。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<vector>
#include<queue>
#define N 5000
#define INF 1000000007
#define T (2*n*m+1)
#define S 0
#define LL long long
#define ri register int
using namespace std;

int n,m,k,opt;

struct graph {
  vector<int> to,w,c;
  vector<int> ed[N];
  LL dis[N]; int cur[N];
  bool vis[N];
  void add_edge(int a,int b,int aw,int ac) {
    to.push_back(b); w.push_back(aw); c.push_back(ac);  ed[a].push_back(to.size()-1);
    to.push_back(a); w.push_back(0);  c.push_back(-ac); ed[b].push_back(to.size()-1);
  }
  bool spfa() {
    memset(dis,-0x3f,sizeof(dis));
    memset(vis,0,sizeof(vis));
    queue<int> q;
    dis[S]=0;q.push(S);vis[S]=1;
    while (!q.empty()) {
      int x=q.front(); q.pop();
      for (ri i=0;i<ed[x].size();i++) {
        int e=ed[x][i];
        if (dis[to[e]]<dis[x]+c[e] && w[e]) {
          dis[to[e]]=dis[x]+c[e];
          if (!vis[to[e]]) vis[to[e]]=1,q.push(to[e]);
        }
      }
      vis[x]=0;
    }
    return dis[T]>-INF;
  }
  int dfs(int x,int lim) {
    if (x==T || !lim) return lim;
    LL sum=0; vis[x]=1;
    for (ri &i=cur[x];i<ed[x].size();i++) {
      int e=ed[x][i];
      if (dis[x]+c[e]==dis[to[e]] && w[e] && !vis[to[e]]) {
        int f=dfs(to[e],min(lim,w[e]));
        w[e]-=f; w[1^e]+=f;
        lim-=f; sum+=f;
        if (!lim) return sum;
      }
    }
    return sum;
  }
  LL zkw() {
    LL ret=0;
    while (spfa()) {
      memset(vis,0,sizeof(vis));
      memset(cur,0,sizeof(cur));
      ret+=dfs(S,INF)*dis[T];
    }
    return ret;
  }
  void print(int col,int tn) {
    if (tn==n*m) return;
    int now=n*m+tn;
    for (ri i=0;i<ed[now].size();i++) {
      int e=ed[now][i];
      if (e%2==1) continue;
      if (c[e]==1 && w[e]==0 || c[e]==0 && w[e]<INF) {
        w[e]++;
        printf("%d %d
",col,to[e]-tn==1?1:0);
        print(col,to[e]);
        return;
      }
    }
  }
} G;

int id1(int x,int y) {return (x-1)*m+y;}
int id2(int x,int y) {return n*m+(x-1)*m+y;}

int main() {
  scanf("%d",&k);
  scanf("%d %d",&n,&m);
  swap(n,m);
  for (ri i=1;i<=n;i++) {
    for (ri j=1;j<=m;j++) {
      scanf("%d",&opt);
      if (opt!=1) {
        G.add_edge(id1(i,j),id2(i,j),INF,0);
        if (opt==2) G.add_edge(id1(i,j),id2(i,j),1,1);
      }
    }
  }
  for (ri i=1;i<=n;i++) {
    for (ri j=1;j<=m;j++) {
      if (i+1<=n) G.add_edge(id2(i,j),id1(i+1,j),INF,0);
      if (j+1<=m) G.add_edge(id2(i,j),id1(i,j+1),INF,0);
    }
  }
  G.add_edge(S,id1(1,1),k,0);
  G.add_edge(id2(n,m),T,k,0);
  int t=G.zkw();
  for (ri i=1;i<=k;i++) G.print(i,1);
  return 0;
}