This program was originally written in October of 2015 for an Algorithms assignment.
This program reads an input file, SpaceStation.txt, which contains data about the start and end times of different projects. Also the number of projects and S and F. The goal is to select a minimum-size set of projects so that at all times from S to F, at least one research project is in progress. The selectProjects function solves this part of the problem.
Each project has an associated cost equal to its length, and the costs of the projects selected must each be charged to one of two accounts. The total costs charged to each account must be as close as possible.
Eg. A totalCost of 100, account1 charged 50 and account2 charged 50 is optimal.
The divideCosts function solves this part of the problem.
This function finds a minimum set of projects that spans from a start time (S) to end time (F).
1. lis: A list of projects
2. lastEnd: The last end time of our result list, starts off as S
How I did this was by creating a temporary list of all the possible values that could be selected, then chose the one with the largest end time value. If we got to the point where the temp list contained a project that ended after the endTime, I selected the one with the least weight.
This function divides the list of projects into two groups so that the cost
of both groups are as close to equal as possible.
1. Takes a list of projects as a paramater
The idea here it to calculate K (totalCost/2) and see if there is a subset in projects that sums to K. If this is true, we determine what projects sum to K and set these as group 1. Group 2 are the projects that sum to totalCost - k. The data is then written to output.txt. If there isn't a subset that sums to K, we try again with K-1.
#!/usr/bin/python import operator #Empty list to hold the start and end time of each project lis =  #Open the input file f = open("SpaceStation.txt") #Holds the number of available projects numProjects = 0 #Holds the start and end time (the range in which we want to fill with projects) startTime = 0 endTime = 0 #Store the input to an appropriate variable or data structure for i, line in enumerate(f): if i == 0: # line 1 holds S and F startTime, endTime = line.split() startTime = int(startTime) endTime = int(endTime) elif i == 1: # line 2 holds the number of projects numProjects = int(line) else: # line > 2 holds the projects start and end times (key, val1, val2) = line.split() lis.append([val1, val2]) #Convert the each element of the list to an integer so that #we can sort it by numerical value. for i in lis: i = int(i) i = int(i) #Make a copy of lis, call it sortedLis. Sorted by the project start time sortedLis = list(lis) sortedLis.sort(key=operator.itemgetter(0)) #Holds the projects that we select as an optimal solution. result =  def selectProjects(lis, lastEnd): """ Finds a minimum set of projects that spans from a start time (S) to end time (F) Paramaters: 1. lis: A lis of projects 2. lastEnd: The last end time of our result list, start off as S """ big = 0 #big will store the largest end time value in our temp list temp =  #Holds potential projects we need to choose from if lastEnd >= endTime or lis == : #We're done, return the result set return result else: i=0 #While start time is before the last chosen end time while lis[i] <= lastEnd: #append project i to the temp list temp.append(lis[i]) if lis[i] == lis[-1]: break i+=1 #Sort temp and lis by end time temp.sort(key=operator.itemgetter(1)) lis.sort(key=operator.itemgetter(1)) #If the last value ends after endTime then we will make our last choice now. #We do this by removing projects that end before endTime and then select the #project with the least weight. if temp[-1] >= endTime: sizeOfTemp = len(temp) j = 0 #remove projects that finish before endTime from temp and lis while j < sizeOfTemp: if temp[j] < endTime: temp.remove(temp[j]) lis.remove(lis[j]) sizeOfTemp-=1 else: j+=1 #Choose the project in temp with the smallest weight #small is initially set to endTime - startTime. It can be set to any large value really. small = endTime - startTime for p in temp: if p - p < small: small = p - p choose = p else: #Re-sort back to sorted by start time. This resolves ties with end times #and chooses the least weighted project (hence the >= big, opposed to just >). temp.sort(key=operator.itemgetter(0)) lis.sort(key=operator.itemgetter(0)) for i in range(len(temp)): if temp[i] >= big: big = temp[i] choose = temp[i] #Append the chosen project to the result list result.append(choose) #Remove the already considered options if temp != : for i in temp: lis.remove(i) selectProjects(lis, result[-1]) def divideCosts(projects): """ This function divides the list of projects into two groups so that the cost of both groups are as close to equal as possible. Parameters: 1. Takes a list of projects as a paramater """ #Holds the costs of each project costList =  #Find the cost of each project, append to costList for i in range(len(projects)): cost = projects[i] - projects[i] costList.append(cost) #Calculate the total Cost totalCost = 0 for i in costList: totalCost += i #Value we want the two costs to be as close to as possible K = totalCost / 2 #We first check if the total cost can be split into K and totalCost - K #If not we check K-1 and (totalCost - (K-1)), and so on.. while K != 0: #If K is a subset sum of costList if subsetSum(costList, K) == True: #DEBUGGING #print str(K) + " and " + str(totalCost - K) L = subsetList(costList, K) #L holds the set of costs of group 1 M = subsetList(costList, totalCost - K) #M holds the set of costs of group 2 group1 =  #Holds the start-end times of the projects of group 1 group2 =  #Holds the start-end times of the projects of group 2 #Append start-end time values to group 1 and group 2 by comparing the #differnce of each set of times in projects with the values in L and M. #If they match, append to the list. for i in projects: for j in L: if i - i == j and i not in group1: group1.append(i) for i in projects: for j in M: if i - i == j and i not in group2: group2.append(i) group1ProjectNums =  #Holds the project # of all the projects in group 1 group2ProjectNums =  #Holds the project # of all the projects in group 2 #Get the project numbers for group 1 as indicated by the first value of #each row in the input file. for i in group1: for j in range(len(lis)): if i == lis[j]: group1ProjectNums.append(j+1) #Get the project numbers for group 2 as indicated by the first value of #each row in the input file. for i in group2: for j in range(len(lis)): if i == lis[j]: group2ProjectNums.append(j+1) #Sort group1ProjectNums and group2ProjectNums group1ProjectNums.sort() group2ProjectNums.sort() #selected projects is equal to the group 1 projects plus the group 2 projects selectedProjects = group1ProjectNums + group2ProjectNums #Sort the list of selected projects selectedProjects.sort() #Print Results to output file, output.txt #Open output.txt in write mode out=open('output.txt', 'w+') #Write results to file out.write("Selected Projects: " + str(selectedProjects)) out.write("\n") out.write("\nGroup 1 Projects: " + str(group1ProjectNums) + ". Total Time: " + str(K)) out.write("\nGroup 2 Projects: " + str(group2ProjectNums) + ". Total Time: " + str(totalCost - K)) break K-=1 """ HELPER FUCNTIONS """ #Given a list and a target, this function returns True or False, whether #there is a subset of lis that sums to target def subsetSum(lis, target): if target == 0: return True for i in range(len(lis)): if subsetSum(lis[:i] + lis[i+1:], target - lis[i]): return True return False #Given a list and a target, this function returns a subset of lis that sums to target. def subsetList(lis, target): subset =  #Holds the result subset for i, x in enumerate(lis): #If subsetSum returns true for the reduced list, and a target of target minus the #value we removed from lis, then append that value(x) because it is in the solution. if subsetSum(lis[i+1:], target - x) == True: subset.append(x) target -= x return subset """ Run Program """ #Call selectProjects with parameters sortedLis (sorted by start time) and startTime (20) selectProjects(sortedLis, startTime) #Call divideCosts with the projects solution list to calculate the total weights #and which projects should be assigned to groups 1 and 2 divideCosts(result)
The input tells us:
-> we need projects running from time 20 to time 100 (line 1)
-> there are 40 projects to choose from (line 2)
-> project number, project start time, project end time (lines 3 -42)
20 100 40 1 58 74 2 12 18 3 75 85 4 48 61 5 93 111 6 84 97 7 1 3 8 58 68 9 43 62 10 40 51 11 28 47 12 6 14 13 59 69 14 47 54 15 18 32 16 9 18 17 90 95 18 87 93 19 35 53 20 38 58 21 78 86 22 18 19 23 97 116 24 57 60 25 50 52 26 57 58 27 53 60 28 49 54 29 76 94 30 15 28 31 34 42 32 86 99 33 82 93 34 70 73 35 54 74 36 51 58 37 23 40 38 70 86 39 49 58 40 22 25
Selected Projects: [1, 5, 9, 11, 15, 32, 38] Group 1 Projects: [5, 9, 11]. Total Time: 56 Group 2 Projects: [1, 15, 32, 38]. Total Time: 59
The output looks good, but we can quickly check it.
|Project||Start Time||End Time|