feat: add non_preemptive_priority_scheduling in Process Scheduling Algorithm (#968)

* Added NonPreemptivePriorityScheduling

* updating DIRECTORY.md

* Added documentation and tests

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Left out documentation and suggested changes

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* test case added with assert.h

* Update process_scheduling_algorithms/non_preemptive_priority_scheduling.c

Co-authored-by: Taj <tjgurwara99@users.noreply.github.com>

* typedef | Snake Case naming

* chore: apply suggestions from code review

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: David Leal <halfpacho@gmail.com>
Co-authored-by: Taj <tjgurwara99@users.noreply.github.com>

DIRECTORY.md

@@ -318,6 +318,9 @@
   * [Simpsons 1 3Rd Rule](https://github.com/TheAlgorithms/C/blob/HEAD/numerical_methods/simpsons_1_3rd_rule.c)
   * [Variance](https://github.com/TheAlgorithms/C/blob/HEAD/numerical_methods/variance.c)
 
+## Process Scheduling Algorithms
+  * [Non Preemptive Priority Scheduling](https://github.com/TheAlgorithms/C/blob/master/process_scheduling_algorithms/non_preemptive_priority_scheduling.c)
+
 ## Project Euler
   * Problem 1
     * [Sol1](https://github.com/TheAlgorithms/C/blob/HEAD/project_euler/problem_1/sol1.c)

process_scheduling_algorithms/non_preemptive_priority_scheduling.c

@@ -0,0 +1,369 @@
+/**
+ * @file
+ * @brief
+ * [Non-Preemptive Priority
+ * Scheduling](https://en.wikipedia.org/wiki/Scheduling_(computing))
+ * is a scheduling algorithm that selects the tasks to execute based on
+ * priority.
+ *
+ * @details
+ * In this algorithm, processes are executed according to their
+ * priority. The process with the highest priority is to be executed first and
+ * so on. In this algorithm, a variable is maintained known as the time quantum.
+ * The length of the time quantum is decided by the user. The process which is
+ * being executed is interrupted after the expiration of the time quantum and
+ * the next process with the highest priority is executed. This cycle of
+ * interrupting the process after every time quantum and resuming the next
+ * process with the highest priority continues until all the processes have
+ * been executed.
+ * @author [Aryan Raj](https://github.com/aryaraj132)
+ */
+#include <assert.h>   /// for assert
+#include <stdbool.h>  /// for boolean data type
+#include <stdio.h>    /// for IO operations (`printf`)
+#include <stdlib.h>  /// for memory allocation eg: `malloc`, `realloc`, `free`, `exit`
+/**
+ * @brief Structure to represent a process
+ */
+ typedef struct node {
+     int ID;             ///< ID of the process node
+     int AT;             ///< Arrival Time of the process node
+     int BT;             ///< Burst Time of the process node
+     int priority;       ///< Priority of the process node
+     int CT;             ///< Completion Time of the process node
+     int WT;             ///< Waiting Time of the process node
+     int TAT;            ///< Turn Around Time of the process node
+     struct node *next;  ///< pointer to the node
+ } node;
+
+/**
+ * @brief To insert a new process in the queue
+ * @param root pointer to the head of the queue
+ * @param id process ID
+ * @param at arrival time
+ * @param bt burst time
+ * @param prior priority of the process
+ * @returns void
+ */
+void insert(node **root, int id, int at, int bt, int prior)
+{
+    // create a new node and initialize it
+    node *new = (node *)malloc(sizeof(node));
+    node *ptr = *root;
+    new->ID = id;
+    new->AT = at;
+    new->BT = bt;
+    new->priority = prior;
+    new->next = NULL;
+    new->CT = 0;
+    new->WT = 0;
+    new->TAT = 0;
+    // if the root is null, make the new node the root
+    if (*root == NULL)
+    {
+        *root = new;
+        return;
+    }
+    // else traverse to the end of the queue and insert the new node there
+    while (ptr->next != NULL)
+    {
+        ptr = ptr->next;
+    }
+    ptr->next = new;
+    return;
+}
+/*
+ * @brief To delete a process from the queue
+ * @param root pointer to the head of the queue
+ * @param id process ID
+ * @returns void
+ */
+void delete(node **root, int id)
+{
+    node *ptr = *root, *prev;
+    // if the root is null, return
+    if (ptr == NULL)
+    {
+        return;
+    }
+    // if the root is the process to be deleted, make the next node the root
+    if (ptr->ID == id)
+    {
+        *root = ptr->next;
+        free(ptr);
+        return;
+    }
+    // else traverse the queue and delete the process
+    while (ptr != NULL && ptr->ID != id)
+    {
+        prev = ptr;
+        ptr = ptr->next;
+    }
+    if (ptr == NULL)
+    {
+        return;
+    }
+    prev->next = ptr->next;
+    free(ptr);
+}
+/**
+ * @brief To show the process queue
+ * @param head pointer to the head of the queue
+ * @returns void
+ */
+void show_list(node *head)
+{
+    printf("Process Priority AT BT CT TAT WT \n");
+    while (head != NULL)
+    {
+        printf("P%d. %d %d %d %d %d %d \n", head->ID, head->priority, head->AT,
+               head->BT, head->CT, head->TAT, head->WT);
+        head = head->next;
+    }
+}
+/**
+ * @brief To length process queue
+ * @param root pointer to the head of the queue
+ * @returns int total length of the queue
+ */
+int l_length(node **root)
+{
+    int count = 0;
+    node *ptr = *root;
+    while (ptr != NULL)
+    {
+        count++;
+        ptr = ptr->next;
+    }
+    return count;
+}
+/**
+ * @brief To update the completion time, turn around time and waiting time of
+ * the processes
+ * @param root pointer to the head of the queue
+ * @param id process ID
+ * @param ct current time
+ * @param wt waiting time
+ * @param tat turn around time
+ * @returns void
+ */
+void update(node **root, int id, int ct, int wt, int tat)
+{
+    node *ptr = *root;
+    // If process to be updated is head node
+    if (ptr != NULL && ptr->ID == id)
+    {
+        if (ct != 0)
+        {
+            ptr->CT = ct;
+        }
+        if (wt != 0)
+        {
+            ptr->WT = wt;
+        }
+        if (tat != 0)
+        {
+            ptr->TAT = tat;
+        }
+        return;
+    }
+    // else traverse the queue and update the values
+    while (ptr != NULL && ptr->ID != id)
+    {
+        ptr = ptr->next;
+    }
+    if (ct != 0)
+    {
+        ptr->CT = ct;
+    }
+    if (wt != 0)
+    {
+        ptr->WT = wt;
+    }
+    if (tat != 0)
+    {
+        ptr->TAT = tat;
+    }
+    return;
+}
+/**
+ * @brief To compare the priority of two processes based on their arrival time
+ * and priority
+ * @param a pointer to the first process
+ * @param b pointer to the second process
+ * @returns true if the priority of the first process is greater than the
+ * the second process
+ * @returns false if the priority of the first process is NOT greater than the
+ * second process
+ */
+bool compare(node *a, node *b)
+{
+    if (a->AT == b->AT)
+    {
+        return a->priority < b->priority;
+    }
+    else
+    {
+        return a->AT < b->AT;
+    }
+}
+/**
+ * @brief To calculate the average completion time of all the processes
+ * @param root pointer to the head of the queue
+ * @returns float average completion time
+ */
+float calculate_ct(node **root)
+{
+    // calculate the total completion time of all the processes
+    node *ptr = *root, *prior, *rpt;
+    int ct = 0, i, time = 0;
+    int n = l_length(root);
+    float avg, sum = 0;
+    node *duproot = NULL;
+    // create a duplicate queue
+    while (ptr != NULL)
+    {
+        insert(&duproot, ptr->ID, ptr->AT, ptr->BT, ptr->priority);
+        ptr = ptr->next;
+    }
+    ptr = duproot;
+    rpt = ptr->next;
+    // sort the queue based on the arrival time and priority
+    while (rpt != NULL)
+    {
+        if (!compare(ptr, rpt))
+        {
+            ptr = rpt;
+        }
+        rpt = rpt->next;
+    }
+    // ptr is the process to be executed first.
+    ct = ptr->AT + ptr->BT;
+    time = ct;
+    sum += ct;
+    // update the completion time, turn around time and waiting time of the
+    // process
+    update(root, ptr->ID, ct, 0, 0);
+    delete (&duproot, ptr->ID);
+    // repeat the process until all the processes are executed
+    for (i = 0; i < n - 1; i++)
+    {
+        ptr = duproot;
+        while (ptr != NULL && ptr->AT > time)
+        {
+            ptr = ptr->next;
+        }
+        rpt = ptr->next;
+        while (rpt != NULL)
+        {
+            if (rpt->AT <= time)
+            {
+                if (rpt->priority < ptr->priority)
+                {
+                    ptr = rpt;
+                }
+            }
+            rpt = rpt->next;
+        }
+        ct += ptr->BT;
+        time += ptr->BT;
+        sum += ct;
+        update(root, ptr->ID, ct, 0, 0);
+        delete (&duproot, ptr->ID);
+    }
+    avg = sum / n;
+    return avg;
+}
+/**
+ * @brief To calculate the average turn around time of all the processes
+ * @param root pointer to the head of the queue
+ * @returns float average turn around time
+ */
+float calculate_tat(node **root)
+{
+    float avg, sum = 0;
+    int n = l_length(root);
+    node *ptr = *root;
+    // calculate the completion time if not already calculated
+    if (ptr->CT == 0)
+    {
+        calculate_ct(root);
+    }
+    // calculate the total turn around time of all the processes
+    while (ptr != NULL)
+    {
+        ptr->TAT = ptr->CT - ptr->AT;
+        sum += ptr->TAT;
+        ptr = ptr->next;
+    }
+    avg = sum / n;
+    return avg;
+}
+/**
+ * @brief To calculate the average waiting time of all the processes
+ * @param root pointer to the head of the queue
+ * @returns float average waiting time
+ */
+float calculate_wt(node **root)
+{
+    float avg, sum = 0;
+    int n = l_length(root);
+    node *ptr = *root;
+    // calculate the completion if not already calculated
+    if (ptr->CT == 0)
+    {
+        calculate_ct(root);
+    }
+    // calculate the total waiting time of all the processes
+    while (ptr != NULL)
+    {
+        ptr->WT = (ptr->TAT - ptr->BT);
+        sum += ptr->WT;
+        ptr = ptr->next;
+    }
+    avg = sum / n;
+    return avg;
+}
+
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void test()
+{
+    // Entered processes
+    // printf("ID Priority Arrival Time Burst Time \n");
+    // printf("1 0 5 1 \n");
+    // printf("2 1 4 2 \n");
+    // printf("3 2 3 3 \n");
+    // printf("4 3 2 4 \n");
+    // printf("5 4 1 5 \n");
+
+    node *root = NULL;
+    insert(&root, 1, 0, 5, 1);
+    insert(&root, 2, 1, 4, 2);
+    insert(&root, 3, 2, 3, 3);
+    insert(&root, 4, 3, 2, 4);
+    insert(&root, 5, 4, 1, 5);
+    float avgCT = calculate_ct(&root);
+    float avgTAT = calculate_tat(&root);
+    float avgWT = calculate_wt(&root);
+    assert(avgCT == 11);
+    assert(avgTAT == 9);
+    assert(avgWT == 6);
+    printf("[+] All tests have successfully passed!\n");
+    // printf("Average Completion Time is : %f \n", calculate_ct(&root));
+    // printf("Average Turn Around Time is : %f \n", calculate_tat(&root));
+    // printf("Average Waiting Time is : %f \n", calculate_wt(&root));
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main()
+{
+    test();  // run self-test implementations
+
+    return 0;
+}