Question

Activity Selection Last-to-Start | C++ Implementation

Develop a program with a greedy algorithm that instead of always selecting the first activity to finish, instead selects the last activity to start that is compatible with all previously selected activities.

The program should read input from a file named “act.txt”. The file contains lists of activity sets with number of activities in the set in the first line followed by lines containing the activity number, start time & finish time.

Example act.txt:
11
1 1 4
2 3 5
3 0 6
4 5 7
5 3 9
6 5 9
7 6 10
8 8 11
9 8 12
10 2 14
11 12 16
3
3 1 8
2 1 2
1 3 9

In the above example the first activity set contains 11 activities with activity 1 starting at time 1 and finishing at time 4, activity 2 starting at time 3 and finishing at time 5, etc.. The second activity set contains 3 activities with activity 3 starting at time 1 and finishing at time 8 etc. Note: the activities in the file are not in any sorted order.

Your results including the number of activities selected and their order should be outputted to the terminal. For the above example the results are:

Set 1
Number of activities selected = 4
Activities: 2 4 8 11

Set 2
Number of activities selected = 2
Activities: 2 1

Answer 1

Solution: Greedy Algorithm: Step 1: Sorted the activities in increasing order of finish times. Step 2: Create a vector to store the chosen activities, and initialized it with the initial activity that has the first finish time. Step 3: Declare a variable 1t' that keeps track of the key of the last selected activity. Step 4: Begins the iterating from second element of that array up to its last element and choose an activity if its start time is greater than the final activity's finish time, therefore the final result providing the optimal solution

C++ Code: # includeくbits/stdc++.h> using namespace std; //main function int main () //read the given file freopen("act.txt", "r", stdin); //declare the variable for at for activities //st for start time and ft for finish time //sn for set number inttt= 1, at, st, ft, sn= 1; int ii while (cin >> tt) //pair template using vector vector>> p; cin >at > st >> ft; p.push back make pai (ft, make pair(st, at))) //sort the activities sort (p.begin),p.end )) //initializes the last lt is 0 //declare the vector variable sd for selected Activities vector sd; //push the selected activities sd.push back (p [0].second.second) LE (p [1]. second. first >= p[lt]. first)

sd.push back(p[i].second.second); It = 1; //print the given result cout << "Set " << sn << endl; cout << "Number of activities selected- " << sa. size() くく "\n"; cout ies: "; for (int i: sd) K<"Activit "\n"; coutくく sntti

act.txt: main.cpp act.txt 2 1 1 4 3 2 3 5 4 3 0 6 5 4 57 6 5 3 9 7 6 5 9 8 7 6 10 9 88 11 10 9 8 12 11 10 2 14 12 11 12 16 13 3 14 3 1 8 15 2 1 2 16 1 3 9 Sample Output: Set 1 Number of activities selected4 Activities: 1 4 8 11 Set 2 Number of activities selected 2 Activities: 2 1

EDITABLE CODE:

#include

using namespace std;

//main function

int main()

{

   //read the given file

   freopen("act.txt", "r", stdin);

   //declare the variable for at for activities

//st for start time and ft for finish time

   //sn for set number

   int tt = 1, at, st, ft, sn = 1;

   int i;

   while (cin >> tt)

   {

       //pair template using vector

       vector>> p;

       for (i = 0; i < tt; ++i)

       {

           cin >> at >> st >> ft;

           p.push_back(make_pair(ft, make_pair(st, at)));     

       }

       //sort the activities

       sort(p.begin(), p.end());

       //initializes the last lt is 0

       int lt = 0;

       //declare the vector variable sd for selected Activities

       vector sd;

       //push the selected activities

       sd.push_back(p[0].second.second);

       for (i = 1; i < tt; ++i)

       {

           if (p[i].second.first >= p[lt].first)

           {

               sd.push_back(p[i].second.second);

               lt = i;

           }

       }

       //print the given result

       cout << "Set " << sn << endl;

       cout << "Number of activities selected = " << sd.size() << "\n";

       cout << "Activities: ";

       for (int i:sd)

       {

           cout << i << " ";

       }

       cout << "\n";

       sn++;

   }

}