feat: add non-preemptive SJF scheduling (#2801)

* Create non_preemptive_sjf_scheduling.cpp

* Update non_preemptive_sjf_scheduling.cpp

Co-authored-by: realstealthninja <[email protected]>

* Update non_preemptive_sjf_scheduling.cpp

Co-authored-by: realstealthninja <[email protected]>

* Update non_preemptive_sjf_scheduling.cpp

Co-authored-by: realstealthninja <[email protected]>

* added a vector to store and print the final result

* Update non_preemptive_sjf_scheduling.cpp

Co-authored-by: realstealthninja <[email protected]>

* Update non_preemptive_sjf_scheduling.cpp

Co-authored-by: realstealthninja <[email protected]>

* 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

Co-authored-by: realstealthninja <[email protected]>

* Update non_preemptive_sjf_scheduling.cpp

* Update non_preemptive_sjf_scheduling.cpp

* Update cpu_scheduling_algorithms/non_preemptive_sjf_scheduling.cpp

Co-authored-by: realstealthninja <[email protected]>

* 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

---------

Co-authored-by: realstealthninja <[email protected]>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

cpu_scheduling_algorithms/non_preemptive_sjf_scheduling.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;
+}