POJ 3281 Dining (Maximum network flow)

Topic Links:

http://poj.org/problem?id=3281

Main topic:

There are n cows, f food, D drinks, the first cow like fi seed food and di kind of drink, each food or drink is selected by a cow, can not be selected by other cows, ask the maximum number of cows to meet the requirements?

Problem Solving Ideas:

The biggest matching problem, the key is how to build a map, can be fictitious out of a source point, a meeting point, altogether need to f+d+2*n+2 points can be, the map is: food-------------------- The cow was opened as a point to allow a cow to correspond to one drink and one food, avoiding the occurrence of a variety of drinks or foods.

Code:

1#include <cstdio>2#include <cstring>3#include <cstdlib>4#include <algorithm>5#include <iostream>6#include <cmath>7#include <queue>8 using namespacestd;9 Ten #defineMAXN 0x3f3f3f3f One #defineN 410 A intMap[n][n], Layer[n], S, e; - BOOLVisit[n]; - BOOLCountlayer (); the intdinic (); -  - intMain () - { +     intN, F, D, X, Y, M; -      while(SCANF (" %d%d%d", &n, &f, &d)! =EOF) +     { As =0, E = f + D + N + N +1; atmemset (Map,0,sizeof(map)); -  -          for(intI=1; i<=f; i++) -map[0][i] =1;//Food and source connections. -  -          for(intI=1; i<=d; i++) inmap[i+f+2*n][e] =1;//drinks and Meeting point links -  to          for(intI=1; i<=n; i++) +Map[i+f][i+f+n] =1;//corresponding cow and ox links -  the          for(intI=1; i<=n; i++) *{//establishing the relationship between cattle and food and drink $             intnum = f +i;Panax Notoginsengscanf ("%d%d", &x, &y); -              while(X--) the             { +scanf ("%d", &m); AMap[m][num] =1; the             } +              while(Y--) -             { $scanf ("%d", &m); $Map[num + n][m+f+2*n] =1; -             } -         } theprintf ("%d\n", Dinic ()); -     }Wuyi     return 0; the } -  Wu BOOLCountlayer () - { AboutDeque <int>Q; $memset (Layer,0,sizeof(Layer)); -layer[0] =1; -Q.push_back (0); -      while(!q.empty ()) A     { +         intnd =Q.front (); the Q.pop_front (); -          for(intI=s; i<=e; i++) $         { the             if(map[nd][i]>0&&!Layer[i]) the             { theLayer[i] = Layer[nd] +1; the                 if(i = =e) -                     return true; in                 Else the Q.push_back (i); the             } About         } the     } the     return false; the } +  - intDinic ()//dinic Templates the {Bayi     intMaxnflow =0, I; the      while(Countlayer ()) the     { -deque<int>Q; -memset (Visit,0,sizeof(visit)); thevisit[0] =1; theQ.push_back (0); the          while(!q.empty ()) the         { -             intnd =Q.back (); the             if(nd! =e) the             { the                  for(i=0; i<=e; i++)94                 { the                     if(map[nd][i]>0&& Layer[i] = = layer[nd]+1&&!Visit[i]) the                     { theVisit[i] =1;98 Q.push_back (i); About                          Break; -                     }101                 }102                 if(I >e)103 Q.pop_back ();104             } the             Else106             {107                 intMinflow =MAXN;108                 intMV;109                  for(i=1; I<q.size (); i++) the                 {111                     intNS = q[i-1]; the                     intNE =Q[i];113                     if(Map[ns][ne] <Minflow) the                     { theMinflow =Map[ns][ne]; theMV =NS;117                     }118                 }119Maxnflow + =Minflow; -                  for(i=1; I<q.size (); i++)121                 {122                     intNS = q[i-1];123                     intNE =Q[i];124Map[ns][ne]-=Minflow; theMap[ne][ns] + =Minflow;126                 }127                  while(! Q.empty () && q.back ()! =mv) - Q.pop_back ();129             } the         }131     } the     returnMaxnflow;133}

POJ 3281 Dining (Maximum network flow)