chore(C): add circular queue (#599)

Co-authored-by: Ming Tsai <37890026+ming-tsai@users.noreply.github.com>

algorithms/C/README.md

@@ -34,6 +34,7 @@
 ## Queues
 
 - [Double Ended Queue using array](queues/double-ended-queue-using-array.c)
+- [Circular Queue using array](queues/circular-queue-using-array.c)
 
 ## Sorting
 

algorithms/C/queues/circular-queue-using-array.c

@@ -0,0 +1,125 @@
+#include <stdio.h>
+#include <stdlib.h>
+#define MAX 10 // size of the array is defined
+
+// global variable
+// using front and rear to keep track of the elements in the queue
+int front = -1, rear = -1, circQueue[MAX];
+
+// function to insert element in the queue
+void enqueue(){
+   int num;
+   printf("Enter the number to be inserted: ");
+   scanf("%d", &num);
+
+   // this means the queue is full and no more element can be inserted
+   if(rear == MAX-1){
+      printf("Overflow");
+   }
+   // queue is empty
+   else if(front == -1 && rear == -1){
+      front = 0;
+      rear = 0;
+   }
+   // reached the end and the beginning index is empty
+   else if(rear == MAX - 1 && front != 0){
+      rear = 0;
+   }
+   else {
+      rear += 1;
+   }
+   //inserting the element at the rear position
+   circQueue[rear] = num;
+}
+
+// function to delete an element from the queue
+void dequeue(){
+   // this means the queue is empty and you cannot take out more elements out of it
+   if(front == -1){
+      printf("Underflow");
+   }
+   // reached the last element
+   else if(front == rear){
+      front = -1;
+      rear = -1;
+   }
+   // reached end of the array since it is circular so front = 0 again.
+   else if(front == MAX - 1){
+      front = 0;
+   }
+   else {
+      front += 1;
+   }
+}
+
+// to print the queue
+void display(){
+    int i;
+    if(front == -1 || rear == -1)
+    {
+        printf("\nEmpty queue\n");
+    }
+    else {
+       printf("The queue is: ");
+       for (i = front; i <= rear; i++){
+       printf("%d ", circQueue[i]);
+    }
+    printf("\n");
+  }
+}
+
+int main()
+{
+    // asking the user for the choice
+    int choice;
+    while(1){
+        printf("Enter your choice: \n1. Enqueue \n2. Dequeue\n3. Display\n4. Exit\n");
+        scanf("%d", &choice);
+
+    switch(choice){
+       case 1:
+          enqueue(); // if user inserts one it will call the enqueue function
+          break;
+       case 2:
+          dequeue();  // if user inserts two it will call the dequeue function
+          break;
+       case 3:
+          display(); //if user inserts three it will print the result
+          break;
+       case 4:
+          return 0;  // exits from the program
+       default:
+          printf("Enter valid choice");
+          break;
+       }
+    }
+    return 0;
+}
+
+/*
+Sample Input:
+1
+3
+1
+3
+1
+3
+2
+3
+
+Sample Output:
+Enter the number to be inserted: 3
+The queue is: 3
+
+Enter the number to be inserted: 5
+The queue is: 5 3
+
+Enter the number to be inserted: 7
+The queue is: 7 5 3
+
+The queue is: 7 5
+
+Time Complexity of Insertion, Deletion: O(1) that is constant
+
+To run the program simply copy the code in a notepad or code editor then save it with extension .c and run it in the terminal using gcc file_name.c or simply run in it in a code editor.
+*/

algorithms/Java/README.md

@@ -1,6 +1,7 @@
 # Java
 
 ## Arrays
+
 - [Counting Inversions](arrays/counting-inversions.java)
 - [Kadanes Algorithm](arrays/kadanes-algorithm.java)
 - [Left Rotation](arrays/left-rotation.java)
@@ -13,9 +14,11 @@
 - [Merge Without Extra Space](arrays/merge-without-extra-space.java)
 
 ## Graphs
+
 - [Dijkstras](graphs/Dijkstras.java)
 
 ## Linked Lists
+
 - [Circular](linked-lists/circular.java)
 - [Clone Linked List](linked-lists/clone-linkedlist.java)
 - [Doubly](linked-lists/doubly.java)
@@ -24,20 +27,24 @@
 - [Fold Linked List](linked-lists/fold-linked-list.java)
 
 ## Maths
+
 - [Factorial](Maths/factorial_using_big_integer.java)
 - [Catalan Numbers](Maths/catalan-numbers.java)
 - [Nth Geek Onacci Number](Maths/nth-geek-onacci-number.java)
 
 ## Queues
+
 - [Circular Queue using Linked List](queues/circular-queue-linked-list.java)
 - [Queue using Linked List](queues/queue-linked-list.java)
 - [Priority Queue using Array](queues/priority-queue-array.java)
 
 ## Scheduling
+
 - [Multi-Level Queue Scheduling](scheduling/multi-level-queue-scheduling.java)
 - [Round Robin](scheduling/round-robin.java)
 
 ## Searching
+
 - [Binary Search](searching/binary-search.java)
 - [Jump Search](searching/jump-search.java)
 - [Linear Search](searching/linear-search.java)
@@ -46,6 +53,7 @@
 - [Interpolation Search](searching/interpolation-search.java)
 
 ## Sorting
+
 - [Bubble Sort](sorting/bubble-sort.java)
 - [Counting Sort](sorting/counting-sort.java)
 - [Heap Sort](sorting/heap-sort.java)
@@ -57,6 +65,7 @@
 - [Cyclic Sort](sorting/cyclic-sort.java)
 
 ## Stacks
+
 - [Balanced Parenthesis](stacks/balanced-paranthesis.java)
 - [Stack](stacks/stack.java)
 - [The Stock Span Problem](stacks/the-stock-span-problem.java)
@@ -64,6 +73,7 @@
 - [Sliding Window Maximum](stacks/sliding-window-maximum.java)
 
 ## Strings
+
 - [KMP](strings/kmp.java)
 - [Palindrome](strings/palindrome.java)
 - [Rabin Krap](strings/rabin-karp.java)
@@ -77,6 +87,7 @@
 - [First Non Repeating Character](strings/first-non-repeating-char.java)
 
 ## Trees
+
 - [Pre in Post Traversal](trees/pre-in-post-traversal.java)
 - [Left View of a Tree](trees/left-view.java)
 - [Right View of a Tree](trees/right-view.java)