【LeetCode】设计数据结构|List、Stack、Queue、DLinkedList
设计链表（中等）
707. 设计链表
冗余版
class MyLinkedList {
class ListNode {
int val;
ListNode next;
ListNode(int val) {
this.val = val;
}
}
int size;
ListNode dummyHead;
public MyLinkedList() {
this.size = 0;
this.dummyHead = new ListNode(-1);
}
public int get(int index) {
if (index + 1 > size) return -1;
ListNode node = dummyHead.next;
for (int i = 0; i < index; i++) {
node = node.next;
}
return node.val;
}
public void addAtHead(int val) {
ListNode newNode = new ListNode(val);
newNode.next = dummyHead.next;
dummyHead.next = newNode;
size++;
}
public void addAtTail(int val) {
ListNode node = dummyHead;
while (node.next != null) {
node = node.next;
}
node.next = new ListNode(val);
size++;
}
public void addAtIndex(int index, int val) {
ListNode newNode = new ListNode(val);
ListNode node = dummyHead;
for (int i = 0; i < index; i++) {
node = node.next;
if (node == null) return;
}
newNode.next = node.next;
node.next = newNode;
size++;
}
public void deleteAtIndex(int index) {
if (index < 0 || index >= size) return;
ListNode node = dummyHead;
for (int i = 0; i < index; i++) {
node = node.next;
}
ListNode deleteNode = node.next;
node.next = deleteNode.next;
// 清除野指针
deleteNode = null;
size--;
}
}
代码复用简化版
class MyLinkedList {
class ListNode {
int val;
ListNode next;
ListNode(int val) {
this.val = val;
}
}
int size;
ListNode dummyHead;
public MyLinkedList() {
this.size = 0;
this.dummyHead = new ListNode(-1);
}
public int get(int index) {
if (index + 1 > size) return -1;
ListNode node = dummyHead.next;
for (int i = 0; i < index; i++) {
node = node.next;
}
return node.val;
}
public void addAtHead(int val) {
this.addAtIndex(0, val);
}
public void addAtTail(int val) {
this.addAtIndex(size, val);
}
public void addAtIndex(int index, int val) {
ListNode newNode = new ListNode(val);
ListNode node = dummyHead;
for (int i = 0; i < index; i++) {
node = node.next;
if (node == null) return;
}
newNode.next = node.next;
node.next = newNode;
size++;
}
public void deleteAtIndex(int index) {
if (index < 0 || index >= size) return;
ListNode node = dummyHead;
for (int i = 0; i < index; i++) {
node = node.next;
}
ListNode deleteNode = node.next;
node.next = deleteNode.next;
// 清除野指针
deleteNode = null;
size--;
}
}
用栈实现队列（简单）
232. 用栈实现队列
class MyQueue {
Stack<Integer> a;
Stack<Integer> b;
public MyQueue() {
this.a = new Stack<Integer>();
this.b = new Stack<Integer>();
}
public void push(int x) {
a.push(x);
}
public int pop() {
if (b.isEmpty()) {
while (!a.isEmpty()) {
b.push(a.pop());
}
}
return b.pop();
}
public int peek() {
if (b.isEmpty()) {
while (!a.isEmpty()) {
b.push(a.pop());
}
}
return b.peek();
}
public boolean empty() {
return a.isEmpty() && b.isEmpty();
}
}
用队列实现栈（简单）
225. 用队列实现栈
方法一：双队列实现
class MyStack {
Queue<Integer> a;
Queue<Integer> b;
public MyStack() {
this.a = new LinkedList<Integer>();
this.b = new LinkedList<Integer>();
}
public void push(int x) {
while (!a.isEmpty()) {
b.offer(a.poll());
}
a.offer(x);
while (!b.isEmpty()) {
a.offer(b.poll());
}
}
public int pop() {
return a.poll();
}
public int top() {
return a.peek();
}
public boolean empty() {
return a.isEmpty();
}
}
方法二：单队列实现
class MyStack {
Queue<Integer> a;
public MyStack() {
this.a = new LinkedList<Integer>();
}
public void push(int x) {
a.offer(x);
for (int i = 0; i < a.size() - 1; i++) {
a.offer(a.poll());
}
}
public int pop() {
return a.poll();
}
public int top() {
return a.peek();
}
public boolean empty() {
return a.isEmpty();
}
}
设计循环队列（中等）
622. 设计循环队列
使用数组实现
class MyCircularQueue {
private int capacity;
private int front, rear;
private int[] elements;
public MyCircularQueue(int k) {
this.capacity = k + 1;
this.front = this.rear = 0;
this.elements = new int[k + 1];
}
public boolean enQueue(int value) {
if (isFull()) return false;
elements[rear] = value;
rear = (rear + 1) % capacity;
return true;
}
public boolean deQueue() {
if (isEmpty()) return false;
front = (front + 1) % capacity;
return true;
}
public int Front() {
return isEmpty() ? -1 : elements[front];
}
public int Rear() {
return isEmpty() ? -1 : elements[(rear - 1 + capacity) % capacity];
}
public boolean isEmpty() {
return rear == front;
}
public boolean isFull() {
return (rear + 1) % capacity == front;
}
}
使用链表实现
class MyCircularQueue {
class ListNode {
int val;
ListNode next;
ListNode(int val) {
this.val = val;
}
}
int capacity, size;
ListNode head, tail;
public MyCircularQueue(int k) {
this.size = 0;
this.capacity = k;
}
public boolean enQueue(int value) {
if (isFull()) return false;
ListNode node = new ListNode(value);
if (isEmpty()) {
head = tail = node;
} else {
tail.next = node;
tail = node;
}
size++;
return true;
}
public boolean deQueue() {
if (isEmpty()) return false;
ListNode node = head;
head = head.next;
node = null;
size--;
return true;
}
public int Front() {
return isEmpty() ? -1 : head.val;
}
public int Rear() {
return isEmpty() ? -1 : tail.val;
}
public boolean isEmpty() {
return size == 0;
}
public boolean isFull() {
return size == capacity;
}
}
设计循环双端队列（中等）
641. 设计循环双端队列
方法一：数组实现
class MyCircularDeque {
private int capacity;
private int front, rear;
private int[] elements;
public MyCircularDeque(int k) {
this.capacity = k + 1;
this.front = this.rear = 0;
this.elements = new int[k + 1];
}
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) % 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() {
return isEmpty() ? -1 : elements[front];
}
public int getRear() {
return isEmpty() ? -1 : elements[(rear - 1 + capacity) % capacity];
}
public boolean isEmpty() {
return front == rear;
}
public boolean isFull() {
return (rear + 1) % capacity == front;
}
}
方法二：链表实现文章来源：https://www.toymoban.com/news/detail-623880.html
class MyCircularDeque {
class DLinkedNode {
int val;
DLinkedNode prev;
DLinkedNode next;
DLinkedNode (int val) {
this.val = val;
}
}
private int size, capacity;
private DLinkedNode dummyHead, dummyTail;
public MyCircularDeque(int k) {
this.size = 0;
this.capacity = k;
// 设置一个虚的头结点和尾节点
this.dummyHead = new DLinkedNode(-1);
this.dummyTail = new DLinkedNode(-1);
this.dummyHead.next = this.dummyTail;
this.dummyTail.prev = this.dummyHead;
}
public boolean insertFront(int value) {
if (isFull()) return false;
DLinkedNode node = new DLinkedNode(value);
node.next = dummyHead.next;
node.prev = dummyHead;
dummyHead.next.prev = node;
dummyHead.next = node;
size++;
return true;
}
public boolean insertLast(int value) {
if (isFull()) return false;
DLinkedNode node = new DLinkedNode(value);
node.next = dummyTail;
node.prev = dummyTail.prev;
dummyTail.prev.next = node;
dummyTail.prev = node;
size++;
return true;
}
public boolean deleteFront() {
if (isEmpty()) return false;
DLinkedNode node = dummyHead.next;
node.next.prev = dummyHead;
dummyHead.next = node.next;
node = null;
size--;
return true;
}
public boolean deleteLast() {
if (isEmpty()) return false;
DLinkedNode node = dummyTail.prev;
node.next.prev = node.prev;
node.prev.next = node.next;
node = null;
size--;
return true;
}
public int getFront() {
return isEmpty() ? -1 : dummyHead.next.val;
}
public int getRear() {
return isEmpty() ? -1 : dummyTail.prev.val;
}
public boolean isEmpty() {
// return dummyHead.next == dummyTail;
// return dummyTail.prev == dummyHead;
return size == 0;
}
public boolean isFull() {
return size == capacity;
}
}
设计前中后队列（中等）
1670. 设计前中后队列文章来源地址https://www.toymoban.com/news/detail-623880.html
class FrontMiddleBackQueue {
// 保持 leftQueue.size() == rightQueue.size()
// or leftQueue.size() + 1 == rightQueue.size()
// 注意中位数是按进入数字流中的数字的先后顺序来看的（别搞反啦！！！）
private LinkedList<Integer> leftQueue;
private LinkedList<Integer> rightQueue;
public FrontMiddleBackQueue() {
leftQueue = new LinkedList<Integer>();
rightQueue = new LinkedList<Integer>();
}
public void pushFront(int val) {
if (leftQueue.size() == rightQueue.size()) {
rightQueue.offerFirst(val);
} else {
leftQueue.offerFirst(rightQueue.pollLast());
rightQueue.offerFirst(val);
}
}
public void pushMiddle(int val) {
if (rightQueue.isEmpty()) {
rightQueue.offerLast(val);
} else if (leftQueue.size() == rightQueue.size()) {
rightQueue.offerLast(val);
} else {
leftQueue.offerFirst(rightQueue.pollLast());
rightQueue.offerLast(val);
}
}
public void pushBack(int val) {
leftQueue.offerLast(val);
if (leftQueue.size() > rightQueue.size()) {
rightQueue.offerLast(leftQueue.pollFirst());
}
}
public int popFront() {
if (rightQueue.isEmpty()) return -1;
int val = rightQueue.pollFirst();
if (leftQueue.size() > rightQueue.size()) {
rightQueue.offerLast(leftQueue.pollFirst());
}
return val;
}
public int popMiddle() {
if (rightQueue.isEmpty()) return -1;
int val = rightQueue.pollLast();
if (leftQueue.size() > rightQueue.size()) {
rightQueue.offerLast(leftQueue.pollFirst());
}
return val;
}
public int popBack() {
if (rightQueue.isEmpty()) return -1;
if (leftQueue.size() < rightQueue.size()) {
leftQueue.offerFirst(rightQueue.pollLast());
}
return leftQueue.pollLast();
}
}
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