knapsack::knapsack(const knapsack &k) // Knapsack copy constructor { numObjects = k.getNumObjects(); costBound = k.getCostBound(); value.resize(numObjects); cost.resize(numObjects); index.resize(numObjects); selected.resize(numObjects); for (int i = 0; i < numObjects; i++) { setValue(i,k.getValue(i)); setCost(i,k.getCost(i)); setIndex(i,k.getIndex(i)); if (k.isSelected(i)) select(i); else unSelect(i); } setNum(k.getNum()); currentValue = k.getCurrentValue(); currentCost = k.getCurrentCost(); }
void branchAndBound(knapsack &k, int maxTime) // Implement a Branch and Bound search for an optimal solution. // Searches for the best decision for objects n and greater, as long // as more than maxTime seconds have not elapsed. Tries // to keep or not keep object n, and then iterates to n+1. Stores // the best solution found so far in bestSolution. { clock_t endTime, startTime = clock(); deque<knapsack> problem; deque<knapsack>::iterator itr; int number,bestValue=0; knapsack bestSolution; double time=0; cout<<"Branching and Bounding"<<endl; // Initially, decisions have not been made about any objects, // so set num = 0. k.setNum(0); // Add the empty knapsack subproblem to the list problem.push_front(k); // Branch and Bound search goes here while (!(problem.empty()) && (time<=maxTime)) //for each object in the deque { k = problem.back(); // current instance is now the last object in the deque while((k.getNum()!=k.getNumObjects()) && (k.bound()> bestValue) && (time<=maxTime)) /*if we haven't considered all the objects left and the bound of the current instance is not worse than our best-so-far solution and we are not out of time*/ { //delete the last object from the deque because we are currently solving it problem.pop_back(); number=k.getNum(); k.setNum(number+1); //we are now considering the next object if(k.getCostBound()-k.getCurrentCost()>k.getCost(number)) { problem.push_back(k); //push the 'don't select' instacne before the take instance k.select(number); } problem.push_back(k); //push the remaining instance endTime=clock();//update current time time=((double)(endTime-startTime))/CLOCKS_PER_SEC; } if (k.getCurrentValue() > bestValue){// replace best values if current ones are better bestValue = k.getCurrentValue(); bestSolution = k; } problem.pop_back(); //delete the last object from the deque since it is fathomed } cout << "Best value found: " << bestValue << endl; cout << bestSolution; k.outFile(bestSolution); }
double greedyKnapsack(knapsack &k){ MaxHeap<float, int>* heap = new MaxHeap<float, int>(&compare); for(int counter = 0; counter < k.getNumObjects(); counter++){ double key = (double) k.getValue(counter) / k.getCost(counter); heap->add(key, counter); } while(! heap->empty()){ int next = heap->extractMaxHeapMaximum(); if(k.getCost(next) + k.getCurrentCost() <= k.getCostBound()){ k.select(next); } } return k.getCurrentValue(); }
void printSolution(knapsack &k, string filename) // Prints out the solution. { ofstream myfile; myfile.open (filename.c_str()); myfile << "------------------------------------------------" << endl; myfile << "Total value: " << k.getCurrentValue() << endl; myfile << "Total cost: " << k.getCurrentCost() << endl << endl; // Print out objects in the solution for (int i = 0; i < k.getNumObjects(); i++) if (k.isSelected(i)) myfile << i << " " << k.getValue(i) << " " << k.getCost(i) << endl; myfile << endl; myfile.close(); }