LeetCode 641. 设计循环双端队列

发布时间:2024年01月05日

难度:Medium

641. 设计循环双端队列

设计实现双端队列。

实现?MyCircularDeque?类:

  • MyCircularDeque(int k)?:构造函数,双端队列最大为?k?。
  • boolean insertFront():将一个元素添加到双端队列头部。 如果操作成功返回?true?,否则返回?false?。
  • boolean insertLast()?:将一个元素添加到双端队列尾部。如果操作成功返回?true?,否则返回?false?。
  • boolean deleteFront()?:从双端队列头部删除一个元素。 如果操作成功返回?true?,否则返回?false?。
  • boolean deleteLast()?:从双端队列尾部删除一个元素。如果操作成功返回?true?,否则返回?false?。
  • int getFront()?):从双端队列头部获得一个元素。如果双端队列为空,返回?-1?。
  • int getRear()?:获得双端队列的最后一个元素。?如果双端队列为空,返回?-1?。
  • boolean isEmpty()?:若双端队列为空,则返回?true?,否则返回?false??。
  • boolean isFull()?:若双端队列满了,则返回?true?,否则返回?false?。

示例 1:

输入
["MyCircularDeque", "insertLast", "insertLast", "insertFront", "insertFront", "getRear", "isFull", "deleteLast", "insertFront", "getFront"]
[[3], [1], [2], [3], [4], [], [], [], [4], []]
输出
[null, true, true, true, false, 2, true, true, true, 4]

解释
MyCircularDeque circularDeque = new MycircularDeque(3); // 设置容量大小为3
circularDeque.insertLast(1);			        // 返回 true
circularDeque.insertLast(2);			        // 返回 true
circularDeque.insertFront(3);			        // 返回 true
circularDeque.insertFront(4);			        // 已经满了,返回 false
circularDeque.getRear();  				// 返回 2
circularDeque.isFull();				        // 返回 true
circularDeque.deleteLast();			        // 返回 true
circularDeque.insertFront(4);			        // 返回 true
circularDeque.getFront();				// 返回 4

提示:

  • 1 <= k <= 1000
  • 0 <= value <= 1000
  • insertFront,?insertLast,?deleteFront,?deleteLast,?getFront,?getRear,?isEmpty,?isFull? 调用次数不大于?2000?次

解法思路:

1. 数组

注意事项:

1)定义指针

  • front:指向队列头部第1个有效数据的位置;
  • rear:指向队列尾部(即最后1个有效数据)的 下一个位置,即下一个从队尾入队元素的位置。

2)队列判空判满

  • 判别队列为空的条件是:front == rear;
  • 判别队列为满的条件是:(rear + 1) % capacity == front;。可以这样理解,当 rear 循环到数组的前面,要从后面追上 front,还差一格的时候,判定队列为满。

3)下标越界

  • 指针后移的时候,下标 +1,要取模;
  • 指针前移的时候,为了循环到数组的末尾,需要先加上数组的长度,然后再对数组长度取模。
2. 链表

法一:

class MyCircularDeque {
    // 数组
    // Time: O(1)
    // Space: O(k)
    private int[] elements;
    private int rear, front;
    private int capacity;

    public MyCircularDeque(int k) {
        capacity = k + 1;
        rear = front = 0;
        elements = new int[capacity];
    }

    public boolean insertFront(int value) {
        if (isFull()) {
            return false;
        }
        front = (front - 1 + capacity) % capacity;
        elements[front] = value;
        return true;
    }

    public boolean insertLast(int value) {
        if (isFull()) {
            return false;
        }
        elements[rear] = value;
        rear = (rear + 1) % capacity;
        return true;
    }

    public boolean deleteFront() {
        if (isEmpty()) {
            return false;
        }
        front = (front + 1) % capacity;
        return true;
    }

    public boolean deleteLast() {
        if (isEmpty()) {
            return false;
        }
        rear = (rear - 1 + capacity) % capacity;
        return true;
    }

    public int getFront() {
        if (isEmpty()) {
            return -1;
        }
        return elements[front];
    }

    public int getRear() {
        if (isEmpty()) {
            return -1;
        }
        return elements[(rear - 1 + capacity) % capacity];
    }

    public boolean isEmpty() {
        return rear == front;
    }

    public boolean isFull() {
        return (rear + 1) % capacity == front;
    }
}

/**
 * Your MyCircularDeque object will be instantiated and called as such:
 * MyCircularDeque obj = new MyCircularDeque(k);
 * boolean param_1 = obj.insertFront(value);
 * boolean param_2 = obj.insertLast(value);
 * boolean param_3 = obj.deleteFront();
 * boolean param_4 = obj.deleteLast();
 * int param_5 = obj.getFront();
 * int param_6 = obj.getRear();
 * boolean param_7 = obj.isEmpty();
 * boolean param_8 = obj.isFull();
 */

?法二:

class MyCircularDeque {
    // 链表
    // Time: O(1)
    // Space: O(k)
    private class Node {
        int val;
        Node prev, next;

        Node(int val) {
            this.val = val;
        }
    }

    private Node head, tail;
    private int capacity;
    private int size;

    public MyCircularDeque(int k) {
        capacity = k;
        size = 0;
    }

    public boolean insertFront(int value) {
        if (size == capacity) {
            return false;
        }
        Node node = new Node(value);
        if (size == 0) {
            head = tail = node;
        } else {
            node.next = head;
            head.prev = node;
            head = node;
        }
        size++;
        return true;
    }

    public boolean insertLast(int value) {
        if (size == capacity) {
            return false;
        }
        Node node = new Node(value);
        if (size == 0) {
            head = tail = node;
        } else {
            tail.next = node;
            node.prev = tail;
            tail = node;
        }
        size++;
        return true;
    }

    public boolean deleteFront() {
        if (size == 0) {
            return false;
        }
        head = head.next;
        if (head != null) {
            head.prev = null;
        }
        size--;
        return true;
    }

    public boolean deleteLast() {
        if (size == 0) {
            return false;
        }
        tail = tail.prev;
        if (tail != null) {
            tail.next = null;
        }
        size--;
        return true;
    }

    public int getFront() {
        if (size == 0) {
            return -1;
        }
        return head.val;
    }

    public int getRear() {
        if (size == 0) {
            return -1;
        }
        return tail.val;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public boolean isFull() {
        return size == capacity;
    }
}

/**
 * Your MyCircularDeque object will be instantiated and called as such:
 * MyCircularDeque obj = new MyCircularDeque(k);
 * boolean param_1 = obj.insertFront(value);
 * boolean param_2 = obj.insertLast(value);
 * boolean param_3 = obj.deleteFront();
 * boolean param_4 = obj.deleteLast();
 * int param_5 = obj.getFront();
 * int param_6 = obj.getRear();
 * boolean param_7 = obj.isEmpty();
 * boolean param_8 = obj.isFull();
 */

文章来源:https://blog.csdn.net/qq_38304915/article/details/135393054
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