added activity selection problem

greedy_approach/activity_selection.c

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+/**
+ * @file
+ * @author [Risanlang Hynniewta](https://github.com/risanlang)
+ * @brief [Activity selection problem](https://en.wikipedia.org/wiki/Activity_selection_problem)
+ * implementation in C to find the Maximum number of activity from the list of given activities.
+ * @details The activity selection problem is a problem concerning the selection of non-conflicting activities to perform within a given time frame,
+ * given a set of activities each marked by a start time (si) and finish time (fi). 
+ * The problem is to select the maximum number of activities that can be performed by a single person or machine using Greedy Tecnique, 
+ * assuming that a person can only work on a single activity at a time.
+ *
+ * To test - run './activity_selection'
+ *Sample Input
+ *Enter the number of activities you have
+ *6
+ *Enter the Start Time of Activity 1 :8
+ *Enter the End Time of Activity 1 :9
+
+ *Enter the Start Time of Activity 2 :5
+ *Enter the End Time of Activity 2 :9
+
+ *Enter the Start Time of Activity 3 :5
+ *Enter the End Time of Activity 3 :7
+
+ *Enter the Start Time of Activity 4 :3
+ *Enter the End Time of Activity 4 :4
+
+ *Enter the Start Time of Activity 5 :0
+ *Enter the End Time of Activity 5 :6
+
+ *Enter the Start Time of Activity 6 :1
+ *Enter the End Time of Activity 6 :2
+
+ *Before Sorting
+ *The start time of activity 1 is : 8
+ *The end time of activity 1 is : 9
+
+ *The start time of activity 2 is : 5
+ *The end time of activity 2 is : 9
+
+ *The start time of activity 3 is : 5
+ *The end time of activity 3 is : 7
+
+ *The start time of activity 4 is : 3
+ *The end time of activity 4 is : 4
+
+ *The start time of activity 5 is : 0
+ *The end time of activity 5 is : 6
+
+ *The start time of activity 6 is : 1
+ *The end time of activity 6 is : 2
+
+ *After Sorting
+ *The start time of activity 1 is : 1
+ *The end time of activity 1 is : 2
+
+ *The start time of activity 2 is : 3
+ *The end time of activity 2 is : 4
+
+ *The start time of activity 3 is : 0
+ *The end time of activity 3 is : 6
+
+ *The start time of activity 4 is : 5
+ *The end time of activity 4 is : 7
+
+ *The start time of activity 5 is : 8
+ *The end time of activity 5 is : 9
+
+ *The start time of activity 6 is : 5
+ *The end time of activity 6 is : 9
+
+ *Following activities are selected
+ *activity with start_time : 1
+ *activity with end_time : 2
+ 
+ *activity with start_time : 3
+ *activity with end_time : 4
+ 
+ *activity with start_time : 5
+ *activity with end_time : 7
+ 
+ *activity with start_time : 8
+ *activity with end_time : 9
+
+ *
+ */
+#include<stdio.h> /// for IO operations
+#include<stdlib.h> /// for Dynamic Memory allocation i.e calloc()
+/// Activity structure with two data members i.e start_time and end_time
+struct activity{
+    int start_time;
+    int end_time;
+};
+
+/**
+ * @brief Printing all the Activity i.e the start_time and end_time of each Activity
+ * @param struct activity *ptr, the pointer to the n activity blocks located in the heap memory
+ * @param n number of activities
+ */
+void printing(struct activity *ptr,int n){
+    for(int i=0;i<n;i++){
+        printf("The start time of activity %d is : %d\n",i+1,(ptr+i)->start_time);
+        printf("The end time of activity %d is : %d\n",i+1,(ptr+i)->end_time);
+        printf("\n");
+    }
+
+}
+
+
+/**
+ * @brief Sorting the activity structure in ascending order of end_time
+ * @param struct activity *ptr, the pointer to the n activity blocks located in the heap 
+ * @param n number of activities
+ */
+void sort_the_structure(struct activity *ptr,int n){
+    struct activity temp;
+    for(int i=0;i<n-1;i++){
+        for(int j=0;j<n-i-1;j++){
+            if((ptr+j)->end_time > (ptr+(j+1))->end_time){
+
+               temp.start_time=(ptr+j)->start_time;
+               temp.end_time=(ptr+j)->end_time;
+
+               (ptr+j)->start_time=(ptr+(j+1))->start_time;
+               (ptr+j)->end_time=(ptr+(j+1))->end_time;
+
+
+                (ptr+(j+1))->start_time=temp.start_time;
+                (ptr+(j+1))->end_time=temp.end_time;
+            }
+        }
+    }
+
+}
+
+
+
+/**
+ * @brief Finding the maximum number of non-conflicting activities to be selected and printing them
+ * @param struct activity *ptr, the pointer to the n activity blocks located in the heap 
+ * @param n number of activities
+ */
+void print_Max_Activities(struct activity *ptr,int n)
+{
+
+    printf("Following activities are selected\n");
+
+    // The first activity always gets selected
+    int i = 0;
+    printf("activity with start_time : %d\n",(ptr+i)->start_time);
+    printf("activity with end_time : %d\n",(ptr+i)->end_time);
+
+
+    // Consider rest of the activities
+    for (int j = 1; j < n; j++) {
+        // If this activity has start time greater than or
+        // equal to the finish time of previously selected
+        // activity, then select it
+        if ((ptr+j)->start_time>= (ptr+i)->end_time) {
+            printf("activity with start_time : %d\n",(ptr+j)->start_time);
+            printf("activity with end_time : %d\n",(ptr+j)->end_time);
+            printf("\n");
+            i = j;
+        }
+    }
+}
+
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main(){
+    int n;
+    struct activity *ptr;
+    printf("Enter the number of activities you have\n");
+    scanf("%d",&n);
+    ptr=(struct activity*)calloc(n,sizeof(struct activity));
+    for(int i=0;i<n;i++){
+        printf("Enter the Start Time of Activity %d :",i+1);
+        scanf("%d",&((ptr+i)->start_time));
+        printf("Enter the End Time of Activity %d :",i+1);
+        scanf("%d",&((ptr+i)->end_time));
+        printf("\n");
+    }
+    printf("Before Sorting\n");
+    printing(ptr,n);
+    sort_the_structure(ptr,n);
+    printf("After Sorting\n");
+    printing(ptr,n);
+    print_Max_Activities(ptr,n);
+    return 0;
+}