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Problem solution · Java

Design Circular Deque

Design Circular Deque: a Java solution using direct simulation. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Direct simulation
Source
walkccc LeetCode Solutions
Length
77 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Direct simulation

For Design Circular Deque, the implementation follows the problem’s operations directly while maintaining only the state needed for the next decision.

  1. Translate each rule into one explicit state update.
  2. Maintain the invariant after every processed item.
  3. Return the accumulated state once all relevant input has been handled.

Code notes

  • 77 lines of Java from the credited upstream file 641.java.
  • The implementation visibly relies on sequence storage, work queue.
  • No explicit loop blocks detected.

Complexity

Count the number and nesting of passes over the input, then include the maintained containers in the memory estimate.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeDesign Circular Deque · JavaJava
Use this to learn the idea, then write your own version.
class MyCircularDeque {  /** Initialize your data structure here. Set the size of the deque to be k. */  public MyCircularDeque(int k) {    this.k = k;    this.q = new int[k];    this.rear = k - 1;  }   /** Adds an item at the front of Deque. Return true if the operation is successful. */  public boolean insertFront(int value) {    if (isFull())      return false;     front = (--front + k) % k;    q[front] = value;    ++size;    return true;  }   /** Adds an item at the rear of Deque. Return true if the operation is successful. */  public boolean insertLast(int value) {    if (isFull())      return false;     rear = ++rear % k;    q[rear] = value;    ++size;    return true;  }   /** Deletes an item from the front of Deque. Return true if the operation is successful. */  public boolean deleteFront() {    if (isEmpty())      return false;     front = ++front % k;    --size;    return true;  }   /** Deletes an item from the rear of Deque. Return true if the operation is successful. */  public boolean deleteLast() {    if (isEmpty())      return false;     rear = (--rear + k) % k;    --size;    return true;  }   /** Get the front item from the deque. */  public int getFront() {    return isEmpty() ? -1 : q[front];  }   /** Get the last item from the deque. */  public int getRear() {    return isEmpty() ? -1 : q[rear];  }   /** Checks whether the circular deque is empty or not. */  public boolean isEmpty() {    return size == 0;  }   /** Checks whether the circular deque is full or not. */  public boolean isFull() {    return size == k;  }   private final int k;  private int[] q;  private int size = 0;  private int front = 0;  private int rear;}

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