Today is Sunday, I gonna review the tasks I've done this week, and finish today's leetcode's April LeetCoding Challenge with cpp.

LeetCode Review

Longest Valid Parentheses

template<typename T>
class reversion_wrapper {
private:
  T& iterable;
public:
  explicit reversion_wrapper(T& iterable): iterable{iterable} {}
  auto begin() const { return std::rbegin(iterable); }
  auto end() const { return std::rend(iterable); }
};

class Solution {
public:
  int longestValidParentheses(string s) {
    int left = 0;
    int right = 0;
    int answer = 0;
    for(auto c : s) {
      if(c == '(') {
        left += 1;
      } else {
        right += 1;
        if(left == right) {
          answer = max(answer, left << 1);
        } else if (left < right) {
          left = 0;
          right = 0;
        }
      }
    }
    left = 0;
    right = 0;
    for(auto c : reversion_wrapper(s)) {
      if(c == ')') {
        right += 1;
      } else {
        left += 1;
        if(left == right) {
          answer = max(answer, left << 1);
        } else if(left > right) {
          left = 0;
          right = 0;
        }
      }
    }
    return answer;
  }
};

April LeetCoding Challenge 4

Description

Design Circular Queue

Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called "Ring Buffer".

One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values.

Implementation the MyCircularQueue class:

• MyCircularQueue(k) Initializes the object with the size of the queue to be k.
• int Front() Gets the front item from the queue. If the queue is empty, return -1.
• int Rear() Gets the last item from the queue. If the queue is empty, return -1.
• boolean enQueue(int value) Inserts an element into the circular queue. Return true if the operation is successful.
• boolean deQueue() Deletes an element from the circular queue. Return true if the operation is successful.
• boolean isEmpty() Checks whether the circular queue is empty or not.
• boolean isFull() Checks whether the circular queue is full or not.

Example 1:

Input
["MyCircularQueue", "enQueue", "enQueue", "enQueue", "enQueue", "Rear", "isFull", "deQueue", "enQueue", "Rear"]
[[3], [1], [2], [3], [4], [], [], [], [4], []]
Output
[null, true, true, true, false, 3, true, true, true, 4]

Explanation
MyCircularQueue myCircularQueue = new MyCircularQueue(3);
myCircularQueue.enQueue(1); // return True
myCircularQueue.enQueue(2); // return True
myCircularQueue.enQueue(3); // return True
myCircularQueue.enQueue(4); // return False
myCircularQueue.Rear();     // return 3
myCircularQueue.isFull();   // return True
myCircularQueue.deQueue();  // return True
myCircularQueue.enQueue(4); // return True
myCircularQueue.Rear();     // return 4

Constraints:

• 1 <= k <= 1000
• 0 <= value <= 1000
• At most 3000 calls will be made to enQueue, deQueue, Front, Rear, isEmpty, and isFull.

Follow up: Could you solve the problem without using the built-in queue?

Solution

class MyCircularQueue {
  int *buffer;
  int begin;
  int capacity;
  int size;
public:
  MyCircularQueue(int k): capacity(k), size(0), begin(0) {
    buffer = new int[capacity];
  }
  
  ~MyCircularQueue() {
    delete[] buffer;
  }

  bool enQueue(int value) {
    if(isFull()) return false;
    buffer[(begin + size) % capacity] = value;
    size += 1;
    return true;
  }

  bool deQueue() {
    if(!size) return false;
    begin += 1;
    begin %= capacity;
    size -= 1;
    return true;
  }

  int Front() {
    if(!size) return -1;
    return buffer[begin];
  }

  int Rear() {
    if(!size) return -1;
    return buffer[(begin + size - 1) % capacity];
  }

  bool isEmpty() {
    return !size;
  }

  bool isFull() {
    return size == capacity;
  }
};