Notes.md

Knowledge from LeetCode

Data Structure

Queue

Circular Queue

A more efficient way is to use a circular queue. Specifically, we may use a fixed-size array and two pointers to indicate the starting position and the ending position. And the goal is to reuse the wasted storage we mentioned previously.

class MyCircularQueue {
private:
    vector<int> data;
    int head;
    int tail;
    int size;
public:
    /** Initialize your data structure here. Set the size of the queue to be k. */
    MyCircularQueue(int k) {
        data.resize(k);
        head = -1;
        tail = -1;
        size = k;
    }
    
    /** Insert an element into the circular queue. Return true if the operation is successful. */
    bool enQueue(int value) {
        if (isFull()) {
            return false;
        }
        if (isEmpty()) {
            head = 0;
        }
        tail = (tail + 1) % size;
        data[tail] = value;
        return true;
    }
    
    /** Delete an element from the circular queue. Return true if the operation is successful. */
    bool deQueue() {
        if (isEmpty()) {
            return false;
        }
        if (head == tail) {
            head = -1;
            tail = -1;
            return true;
        }
        head = (head + 1) % size;
        return true;
    }
    
    /** Get the front item from the queue. */
    int Front() {
        if (isEmpty()) {
            return -1;
        }
        return data[head];
    }
    
    /** Get the last item from the queue. */
    int Rear() {
        if (isEmpty()) {
            return -1;
        }
        return data[tail];
    }
    
    /** Checks whether the circular queue is empty or not. */
    bool isEmpty() {
        return head == -1;
    }
    
    /** Checks whether the circular queue is full or not. */
    bool isFull() {
        return ((tail + 1) % size) == head;
    }
};