feat: improve the Singly Link List implementation (#1092)

* Update singly_link_list_deletion.c

Delete function is updated to delete at any required position (not only first)

* Update singly_link_list_deletion.c

The code is changed as per the suggestions. Please lat me know if there are any changes to be done
Thank you

* Update singly_link_list_deletion.c

The code is changed as per the suggestions. Please let me know if there are any changes to be done
Thank you..

* Update singly_link_list_deletion.c

I added inserting at any input location . Please let me know if changes need to be done

* Update singly_link_list_deletion.c

* Update singly_link_list_deletion.c

I updated self tests for both insert and delete functions properly. Please let me know if any changes need to be done
Thank you

* Update singly_link_list_deletion.c

As per your suggestions I updated the code. Please let me know if any changes need to be done..

* chore: apply suggestions from code review

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

data_structures/linked_list/singly_link_list_deletion.c

@@ -4,39 +4,64 @@
   when passed with a key of the node.
 */
 #include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
 struct node
 {
     int info;
     struct node *link;
 };
 struct node *start = NULL;
-///////////////////////////////////////////////////////////
+//////////////////////////////////////////////////////////////////
 struct node *createnode() // function to create node
 {
     struct node *t;
     t = (struct node *)malloc(sizeof(struct node));
     return (t);
 }
-////////////////////////////////////////////////////////
-void insert()  // function to insert at first location
+//////////////////////////////////////////////////////////////////
+int insert(int pos, int d)
 {
-    struct node *p;
-    p = createnode();
-    printf("\nenter the number to insert");
-    scanf("%d", &p->info);
-    p->link = NULL;
+    struct node *new;
+    new = createnode();
+    new->info = d;
+    if (pos == 1)
+    {
+        new->link = NULL;
         if (start == NULL)
         {
-        start = p;
+            start = new;
         }
         else
         {
-        p->link = start;
-        start = p;
+            new->link = start;
+            start = new;
         }
-}
-///////////////////////////////////////////////////////////
-void deletion()  // function to delete from first position
+    }
+    else
+    {
+        struct node *pre = start;
+        for (int i = 2; i < pos; i++)
+        {
+             if (pre == NULL)
+            {
+                break;
+            }
+            pre = pre->link;
+        }
+        if(pre==NULL)
+        {
+            printf("Position not found!");
+            return 0;
+        }
+        new->link = pre->link;
+        pre->link = new;
+    }
+    return 0;
+        }
+
+///////////////////////////////////////////////////////////////////
+int deletion(int pos) // function to delete from any position
 {
     struct node *t;
     if (start == NULL)
@@ -44,14 +69,34 @@ void deletion()  // function to delete from first position
         printf("\nlist is empty");
     }
     else
+    {
+        if (pos == 1)
         {
             struct node *p;
             p = start;
             start = start->link;
             free(p);
         }
+        else
+        {
+            struct node *prev = start;
+            for (int i = 2; i < pos; i++)
+            {
+                if (prev == NULL)
+                {
+                    printf("Position not found!");
+                    return 0;
+                }
+                prev = prev->link;
+            }
+            struct node *n = prev->link; // n points to required node to be deleted
+            prev->link = n->link;
+            free(n);
+        }
+    }
+    return 0;
 }
-///////////////////////////////////////////////////////
+///////////////////////////////////////////////////////////////////
 void viewlist() // function to display values
 {
     struct node *p;
@@ -69,25 +114,52 @@ void viewlist()  // function to display values
         }
     }
 }
-//////////////////////////////////////////////////////////////////////
+//////////////////////////////////////////////////////////////////
+static void test()
+{
+    insert(1, 39);
+    assert(start->info == 39);
+    insert(2, 10);
+    insert(3, 11);
+    deletion(1);
+    assert(start->info != 39);
 
+    printf("Self-tests successfully passed!\n");
+}
+//////////////////////////////////////////////////////////////////
 int main()
 {
-    int n;
+    int n = 0, pos = 0, p = 0, num = 0, c = 0;
+    printf("\n1.self test mode");
+    printf("\n2.interactive mode");
+    printf("\nenter your choice:");
+    scanf("%d", &c);
+    if (c == 1)
+    {
+        test();
+    }
+    else if (c == 2)
+    {
         while (1)
         {
-        printf("\n1.add value at first location");
-        printf("\n2.delete value from first location");
-        printf("\n3.view value");
-        printf("\nenter your choice");
+            printf("\n1.add value at the given location");
+            printf("\n2.delete value at the given location");
+            printf("\n3.view list");
+            printf("\nenter your choice :");
             scanf("%d", &n);
             switch (n)
             {
             case 1:
-            insert();
+                printf("enter the position where the element is to be added :");
+                scanf("%d", &p);
+                printf("enter the element is to be added :");
+                scanf("%d", &num);
+                insert(p, num);
                 break;
             case 2:
-            deletion();
+                printf("enter the position where the element is to be deleted :");
+                scanf("%d", &pos);
+                deletion(pos);
                 break;
             case 3:
                 viewlist();
@@ -96,5 +168,10 @@ int main()
                 printf("\ninvalid choice");
             }
         }
-    return (0);
+    }
+    else
+    {
+        printf("Invalid choice");
+    }
+    return 0;
 }