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feat: add non-preemptive SJF scheduling (#2801)
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* Create non_preemptive_sjf_scheduling.cpp

* Update non_preemptive_sjf_scheduling.cpp

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* Update non_preemptive_sjf_scheduling.cpp

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* Update non_preemptive_sjf_scheduling.cpp

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* added a vector to store and print the final result

* Update non_preemptive_sjf_scheduling.cpp

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* Update non_preemptive_sjf_scheduling.cpp

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* Create non_preemptive_sjf_scheduling.cpp

I have done the necessary changes.
The test function will generate 10 different testcases in which it will print  the before and after the SJF scheduling.

@realstealthninja Kindly review the PR and please accept it.

* Delete non_preemptive_sjf_scheduling.cpp

* Update cpu_scheduling_algorithms/non_preemptive_sjf_scheduling.cpp

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* Update non_preemptive_sjf_scheduling.cpp

* Update non_preemptive_sjf_scheduling.cpp

* Update cpu_scheduling_algorithms/non_preemptive_sjf_scheduling.cpp

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* Update non_preemptive_sjf_scheduling.cpp

* Update non_preemptive_sjf_scheduling.cpp

* clang-format and clang-tidy fixes for 57e670c

* chore: remove spaces

* Update dynamic_programming/unbounded_0_1_knapsack.cpp

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/**
* @file
* @brief Implementation of SJF CPU scheduling algorithm
* @details
* shortest job first (SJF), also known as shortest job next (SJN), is a
* scheduling policy that selects for execution the waiting process with the
* smallest execution time. SJN is a non-preemptive algorithm. Shortest
* remaining time is a preemptive variant of SJN.
* <a href="https://www.guru99.com/shortest-job-first-sjf-scheduling.html">
* detailed description on SJF scheduling </a>
* <a href="https://github.com/LakshmiSrikumar">Author : Lakshmi Srikumar </a>
*/

#include <algorithm> /// for sorting
#include <cassert> /// for assert
#include <iomanip> /// for formatting the output
#include <iostream> /// for IO operations
#include <queue> /// for std::priority_queue
#include <random> /// random number generation
#include <unordered_set> /// for std::unordered_set
#include <vector> /// for std::vector

using std::cin;
using std::cout;
using std::endl;
using std::get;
using std::left;
using std::make_tuple;
using std::priority_queue;
using std::tuple;
using std::unordered_set;
using std::vector;

/**
* @brief Comparator function for sorting a vector
* @tparam S Data type of Process ID
* @tparam T Data type of Arrival time
* @tparam E Data type of Burst time
* @param t1 First tuple<S,T,E>t1
* @param t2 Second tuple<S,T,E>t2
* @returns true if t1 and t2 are in the CORRECT order
* @returns false if t1 and t2 are in the INCORRECT order
*/
template <typename S, typename T, typename E>
bool sortcol(tuple<S, T, E>& t1, tuple<S, T, E>& t2) {
if (get<1>(t1) < get<1>(t2) ||
(get<1>(t1) == get<1>(t2) && get<0>(t1) < get<0>(t2))) {
return true;
}
return false;
}

/**
* @class Compare
* @brief Comparator class for priority queue
* @tparam S Data type of Process ID
* @tparam T Data type of Arrival time
* @tparam E Data type of Burst time
*/
template <typename S, typename T, typename E>
class Compare {
public:
/**
* @param t1 First tuple
* @param t2 Second tuple
* @brief A comparator function that checks whether to swap the two tuples
* or not.
* <a
* href="https://www.geeksforgeeks.org/comparator-class-in-c-with-examples/">
* detailed description of comparator </a>
* @returns true if the tuples SHOULD be swapped
* @returns false if the tuples SHOULDN'T be swapped
*/
bool operator()(tuple<S, T, E, double, double, double>& t1,
tuple<S, T, E, double, double, double>& t2) {
// Compare burst times for SJF
if (get<2>(t2) < get<2>(t1)) {
return true;
}
// If burst times are the same, compare arrival times
else if (get<2>(t2) == get<2>(t1)) {
return get<1>(t2) < get<1>(t1);
}
return false;
}
};

/**
* @class SJF
* @brief Class which implements the SJF scheduling algorithm
* @tparam S Data type of Process ID
* @tparam T Data type of Arrival time
* @tparam E Data type of Burst time
*/
template <typename S, typename T, typename E>
class SJF {
/**
* Priority queue of schedules(stored as tuples) of processes.
* In each tuple
* @tparam 1st element: Process ID
* @tparam 2nd element: Arrival Time
* @tparam 3rd element: Burst time
* @tparam 4th element: Completion time
* @tparam 5th element: Turnaround time
* @tparam 6th element: Waiting time
*/
priority_queue<tuple<S, T, E, double, double, double>,
vector<tuple<S, T, E, double, double, double>>,
Compare<S, T, E>>
schedule;

// Stores final status of all the processes after completing the execution.
vector<tuple<S, T, E, double, double, double>> result;

// Stores process IDs. Used for confirming absence of a process while it.
unordered_set<S> idList;

public:
/**
* @brief Adds the process to the ready queue if it isn't already there
* @param id Process ID
* @param arrival Arrival time of the process
* @param burst Burst time of the process
* @returns void
*
*/
void addProcess(S id, T arrival, E burst) {
// Add if a process with process ID as id is not found in idList.
if (idList.find(id) == idList.end()) {
tuple<S, T, E, double, double, double> t =
make_tuple(id, arrival, burst, 0, 0, 0);
schedule.push(t);
idList.insert(id);
}
}

/**
* @brief Algorithm for scheduling CPU processes according to
* the Shortest Job First (SJF) scheduling algorithm.
*
* @details Non pre-emptive SJF is an algorithm that schedules processes
* based on the length of their burst times. The process with the smallest
* burst time is executed first.In a non-preemptive scheduling algorithm,
* once a process starts executing,it runs to completion without being
* interrupted.
*
* I used a min priority queue because it allows you to efficiently pick the
* process with the smallest burst time in constant time, by maintaining a
* priority order where the shortest burst process is always at the front.
*
* @returns void
*/

vector<tuple<S, T, E, double, double, double>> scheduleForSJF() {
// Variable to keep track of time elapsed so far
double timeElapsed = 0;

while (!schedule.empty()) {
tuple<S, T, E, double, double, double> cur = schedule.top();

// If the current process arrived at time t2, the last process
// completed its execution at time t1, and t2 > t1.
if (get<1>(cur) > timeElapsed) {
timeElapsed += get<1>(cur) - timeElapsed;
}

// Add Burst time to time elapsed
timeElapsed += get<2>(cur);

// Completion time of the current process will be same as time
// elapsed so far
get<3>(cur) = timeElapsed;

// Turnaround time = Completion time - Arrival time
get<4>(cur) = get<3>(cur) - get<1>(cur);

// Waiting time = Turnaround time - Burst time
get<5>(cur) = get<4>(cur) - get<2>(cur);

// Turnaround time >= Burst time
assert(get<4>(cur) >= get<2>(cur));

// Waiting time is never negative
assert(get<5>(cur) >= 0);

result.push_back(cur);
schedule.pop();
}
return result;
}
/**
* @brief Utility function for printing the status of
* each process after execution
* @returns void
*/

void printResult(
const vector<tuple<S, T, E, double, double, double>>& processes) {
cout << std::setw(17) << left << "Process ID" << std::setw(17) << left
<< "Arrival Time" << std::setw(17) << left << "Burst Time"
<< std::setw(17) << left << "Completion Time" << std::setw(17)
<< left << "Turnaround Time" << std::setw(17) << left
<< "Waiting Time" << endl;

for (const auto& process : processes) {
cout << std::setprecision(2) << std::fixed << std::setw(17) << left
<< get<0>(process) << std::setw(17) << left << get<1>(process)
<< std::setw(17) << left << get<2>(process) << std::setw(17)
<< left << get<3>(process) << std::setw(17) << left
<< get<4>(process) << std::setw(17) << left << get<5>(process)
<< endl;
}
}
};

/**
* @brief Computes the final status of processes after
* applying non-preemptive SJF scheduling
* @tparam S Data type of Process ID
* @tparam T Data type of Arrival time
* @tparam E Data type of Burst time
* @param input A vector of tuples containing Process ID, Arrival time, and
* Burst time
* @returns A vector of tuples containing Process ID, Arrival time, Burst time,
* Completion time, Turnaround time, and Waiting time
*/
template <typename S, typename T, typename E>
vector<tuple<S, T, E, double, double, double>> get_final_status(
vector<tuple<S, T, E>> input) {
// Sort the processes based on Arrival time and then Burst time
sort(input.begin(), input.end(), sortcol<S, T, E>);

// Result vector to hold the final status of each process
vector<tuple<S, T, E, double, double, double>> result(input.size());
double timeElapsed = 0;

for (size_t i = 0; i < input.size(); i++) {
// Extract Arrival time and Burst time
T arrival = get<1>(input[i]);
E burst = get<2>(input[i]);

// If the CPU is idle, move time to the arrival of the next process
if (arrival > timeElapsed) {
timeElapsed = arrival;
}

// Update timeElapsed by adding the burst time
timeElapsed += burst;

// Calculate Completion time, Turnaround time, and Waiting time
double completion = timeElapsed;
double turnaround = completion - arrival;
double waiting = turnaround - burst;

// Store the results in the result vector
result[i] = make_tuple(get<0>(input[i]), arrival, burst, completion,
turnaround, waiting);
}

return result;
}

/**
* @brief Self-test implementations
* @returns void
*/
static void test() {
// A vector to store the results of all processes across all test cases.
vector<tuple<uint32_t, uint32_t, uint32_t, double, double, double>>
finalResult;

for (int i{}; i < 10; i++) {
std::random_device rd; // Seeding
std::mt19937 eng(rd());
std::uniform_int_distribution<> distr(1, 10);

uint32_t n = distr(eng);
SJF<uint32_t, uint32_t, uint32_t> readyQueue;
vector<tuple<uint32_t, uint32_t, uint32_t, double, double, double>>
input(n);

// Generate random arrival and burst times
for (uint32_t i{}; i < n; i++) {
get<0>(input[i]) = i;
get<1>(input[i]) = distr(eng); // Random arrival time
get<2>(input[i]) = distr(eng); // Random burst time
}

// Print processes before scheduling
cout << "Processes before SJF scheduling:" << endl;
readyQueue.printResult(input);

// Add processes to the queue
for (uint32_t i{}; i < n; i++) {
readyQueue.addProcess(get<0>(input[i]), get<1>(input[i]),
get<2>(input[i]));
}

// Perform SJF schedulings
auto finalResult = readyQueue.scheduleForSJF();

// Print processes after scheduling
cout << "\nProcesses after SJF scheduling:" << endl;
readyQueue.printResult(finalResult);
}
cout << "All the tests have successfully passed!" << endl;
}

/**
* @brief Main function
* @returns 0 on successful exit
*/
int main() {
test();
return 0;
}

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