leastcostbbboard.cpp

《数据结构、算法与应用》从C++语言应用角度列举了要点

// least-cost branch-and-bound method to find best board arrangement

#include <iostream>
#include "minHeap.h"
#include "make2dArrayNoCatch.h"

struct heapNode
{
   // data members
   int partialDensity;             // density of partial arrangement
   int *boardsInPartialWithNet; 
   int sizeOfPartial;       // partial arrangement is
                            // partial[1:sizeOfPartial]
   int *partial;            // partial[sizeOfPartial+1:numberOfBoards]
                            // gives remaining boards
                            // to be added to partial[1:sizeOfPartial]

   // constructors
   heapNode() {}

   heapNode(int thePartialDensity,
            int *theBoardsInPartialWithNet,
            int theSizeOfPartial,
            int *thePartial)
   {
      partialDensity = thePartialDensity;
      boardsInPartialWithNet = theBoardsInPartialWithNet;
      sizeOfPartial = theSizeOfPartial;
      partial = thePartial;
   }

   operator int() {return partialDensity;}

   operator>(const heapNode right)
      {return partialDensity > right.partialDensity;}
};

int leastCostBBBoards(int **board, int numberOfBoards, int numberOfNets,
                      int *bestPermutation)
{// Least-cost branch-and-bound code.
 // Return density of best arrangement.
   minHeap<heapNode> liveNodeMinHeap;

   // initialize first E-node (partialDensity,
   // boardsInPartialWithNet, sizeOfPartial, partial)
   heapNode eNode(0, new int [numberOfNets + 1],
                  0, new int [numberOfBoards + 1]);

   // set eNode.boardsInPartialWithNet[i] = number of boards
   // in partial[1:s] with net i
   // set eNode.partial[i] = i, initial permutation
   // set eNode.boardsWithNet[i] = number of boards with net i
   int *boardsWithNet = new int [numberOfNets + 1];
   fill (boardsWithNet + 1, boardsWithNet + numberOfNets + 1, 0);
   for (int i = 1; i <= numberOfBoards; i++)
   {
      eNode.partial[i] = i;
      eNode.boardsInPartialWithNet[i] = 0;
      for (int j = 1; j <= numberOfNets; j++)
         boardsWithNet[j] += board[i][j];
   }

   int leastDensitySoFar = numberOfNets + 1;
   int *bestPermutationSoFar = NULL;
   
   do
   {// expand E-node
      if (eNode.sizeOfPartial == numberOfBoards - 1)
      {// one child only
         int localDensityAtLastBoard = 0;
         for (int j = 1; j <= numberOfNets; j++)
            localDensityAtLastBoard +=
                 board[eNode.partial[numberOfBoards]][j];
         if (localDensityAtLastBoard < leastDensitySoFar)
         {// better permutation
            bestPermutationSoFar = eNode.partial;
            eNode.partial = NULL;
            leastDensitySoFar = max(localDensityAtLastBoard,
                                    eNode.partialDensity);
         }
      }
      else
      {// generate children of E-node
         for (int i = eNode.sizeOfPartial + 1; i <= numberOfBoards; i++)
         {
            heapNode hNode(0, new int [numberOfNets + 1],
                           0, new int [numberOfBoards + 1]);
            for (int j = 1; j <= numberOfNets; j++)
               // acccount for nets in new board
               hNode.boardsInPartialWithNet[j] =
                                  eNode.boardsInPartialWithNet[j]
                                  + board[eNode.partial[i]][j];

            int localDensityAtNewBoard = 0;
            for (int j = 1; j <= numberOfNets; j++)
               if (hNode.boardsInPartialWithNet[j] > 0 &&
                 boardsWithNet[j] != hNode.boardsInPartialWithNet[j])
                  localDensityAtNewBoard++;

            hNode.partialDensity = max(localDensityAtNewBoard,
                                       eNode.partialDensity);
            if (hNode.partialDensity < leastDensitySoFar)
            {// may lead to better leaf
               hNode.sizeOfPartial = eNode.sizeOfPartial + 1;
               for (int j = 1; j <= numberOfBoards; j++)
                  hNode.partial[j] = eNode.partial[j];
               hNode.partial[hNode.sizeOfPartial] = eNode.partial[i];
               hNode.partial[i] = eNode.partial[hNode.sizeOfPartial];
               liveNodeMinHeap.push(hNode);
            }
         }
      }

      // next E-node
      delete [] eNode.partial;
      delete [] eNode.boardsInPartialWithNet;
      if (liveNodeMinHeap.empty()) break;
      eNode = liveNodeMinHeap.top();
      liveNodeMinHeap.pop();
   } while (eNode.partialDensity < leastDensitySoFar);
   
   for (int i = 1; i <= numberOfBoards; i++)
      bestPermutation[i] = bestPermutationSoFar[i];
   return leastDensitySoFar;
}

void main()
{
   // input number of boards and nets
   cout << "Enter number of boards and number of nets" << endl;
   int n, m;
   cin >> n >> m;

   // define and input board array
   int **board;
   make2dArray(board, n + 1, n + 1);
   cout << "Enter net matrix" << endl;
   for (int i = 1; i <= n; i++) 
      for (int j = 1; j <= m; j++)
         cin >> board[i][j];

   // define array for best board arrangement
   int *p = new int [n + 1];

   cout << "\nMinimum density is " << leastCostBBBoards(board, n, m, p) << endl;
   cout << "Optimal arrangement is ";
   copy(p + 1, p + n + 1, ostream_iterator<int>(cout, "  "));
   cout << endl;
}