luc064.c

Metadata

• Author — Amit Dutta
• Last updated — 08 Feb 2026
• License — MIT License (See the LICENSE file for details)

Problem Statement

Problem Statement

Simulate a Dequeue (Double Ended Queue) using an array. Support: retrieve left, retrieve right, insert left, insert right. Use pointers left and right.

Source Code

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#include <stdio.h>
#include <math.h>
#include <stdlib.h>

#define MAX 10

void insert_left(int *, int *, int *, int);
void insert_right(int *, int *, int *, int);
void retrieve_left(int *, int *, int *);
void retrieve_right(int *, int *, int *);
void display(int *, int, int);

int main()
{
    int dq[MAX];
    int left = -1, right = -1;
    int choice, val;

    while (1)
    {
        printf("\n--- Dequeue Menu ---\n");
        printf("1. Insert Left\n2. Insert Right\n");
        printf("3. Retrieve Left\n4. Retrieve Right\n");
        printf("5. Display\n6. Exit\n");
        printf("Enter choice: ");
        scanf("%d", &choice);

        switch (choice)
        {
        case 1:
            printf("Enter value: ");
            scanf("%d", &val);
            insert_left(dq, &left, &right, val);
            break;
        case 2:
            printf("Enter value: ");
            scanf("%d", &val);
            insert_right(dq, &left, &right, val);
            break;
        case 3:
            retrieve_left(dq, &left, &right);
            break;
        case 4:
            retrieve_right(dq, &left, &right);
            break;
        case 5:
            display(dq, left, right);
            break;
        case 6:
            exit(0);
        default:
            printf("Invalid choice!\n");
        }
    }
    return 0;
}

void insert_left(int *dq, int *left, int *right, int val)
{
    // Check if full
    if ((*left == 0 && *right == MAX - 1) || (*left == *right + 1))
    {
        printf("Overflow! Dequeue is full.\n");
        return;
    }

    if (*left == -1) // Initially empty
    {
        *left = 0;
        *right = 0;
    }
    else if (*left == 0) // Wrap around
        *left = MAX - 1;
    else
        (*left)--;

    dq[*left] = val;
    printf("Inserted %d at Left.\n", val);
}

void insert_right(int *dq, int *left, int *right, int val)
{
    if ((*left == 0 && *right == MAX - 1) || (*left == *right + 1))
    {
        printf("Overflow! Dequeue is full.\n");
        return;
    }

    if (*left == -1) // Initially empty
    {
        *left = 0;
        *right = 0;
    }
    else if (*right == MAX - 1) // Wrap around
        *right = 0;
    else
        (*right)++;

    dq[*right] = val;
    printf("Inserted %d at Right.\n", val);
}

void retrieve_left(int *dq, int *left, int *right)
{
    if (*left == -1)
    {
        printf("Underflow! Dequeue is empty.\n");
        return;
    }

    printf("Retrieved from Left: %d\n", dq[*left]);

    if (*left == *right) // Only one element was present
    {
        *left = -1;
        *right = -1;
    }
    else if (*left == MAX - 1)
        *left = 0;
    else
        (*left)++;
}

void retrieve_right(int *dq, int *left, int *right)
{
    if (*left == -1)
    {
        printf("Underflow! Dequeue is empty.\n");
        return;
    }

    printf("Retrieved from Right: %d\n", dq[*right]);

    if (*left == *right) // Only one element was present
    {
        *left = -1;
        *right = -1;
    }
    else if (*right == 0)
        *right = MAX - 1;
    else
        (*right)--;
}

void display(int *dq, int left, int right)
{
    int i;
    if (left == -1)
    {
        printf("Dequeue is Empty\n");
        return;
    }

    printf("Elements: ");
    i = left;
    while (1)
    {
        printf("%d ", dq[i]);
        if (i == right)
            break;
        if (i == MAX - 1)
            i = 0;
        else
            i++;
    }
    printf("\n");
}