（链表栈队列递归）

文章目录

- 链表
- - - 反转链表
    - 删除点链表中给定值的结点
- 栈和队列
- - - 双向链表实现栈和队列
    - 数组实现队列
    - 获取栈的最小值
    - 用两个栈实现一个队列
    - 用两个队列实现一个栈
- 递归

链表

反转链表

（反转单链表反转双向链表）

public class Code01_ReverseList {public static class Node {public int value;public Node next;public Node(int data) {value = data;}}public static class DoubleNode {public int value;public DoubleNode last;public DoubleNode next;public DoubleNode(int data) {value = data;}}//  head//   a    ->   b    ->  c  ->  null//   c    ->   b    ->  a  ->  nullpublic static Node reverseLinkedList(Node head) {Node pre = null;Node next = null;while (head != null) {next = head.next;head.next = pre;pre = head;head = next;}return pre;}public static DoubleNode reverseDoubleList(DoubleNode head) {DoubleNode pre = null;DoubleNode next = null;while (head != null) {next = head.next;head.next = pre;head.last = next;pre = head;head = next;}return pre;}
}

删除点链表中给定值的结点

public class Code02_DeleteGivenValue {public static class Node {public int value;public Node next;public Node(int data) {this.value = data;}}// head = removeValue(head, 2);public static Node removeValue(Node head, int num) {// head来到第一个不需要删的位置while (head != null) {if (head.value != num) {break;}head = head.next;}// 1 ) head == null// 2 ) head != nullNode pre = head;Node cur = head;while (cur != null) {if (cur.value == num) {pre.next = cur.next;} else {pre = cur;}cur = cur.next;}return head;}
}

栈和队列

双向链表实现栈和队列

public class Code03_DoubleEndsQueueToStackAndQueue {public static class Node<T> {public T value;public Node<T> last;public Node<T> next;public Node(T data) {value = data;}}public static class DoubleEndsQueue<T> {public Node<T> head;public Node<T> tail;public void addFromHead(T value) {Node<T> cur = new Node<T>(value);if (head == null) {head = cur;tail = cur;} else {cur.next = head;head.last = cur;head = cur;}}public void addFromBottom(T value) {Node<T> cur = new Node<T>(value);if (head == null) {head = cur;tail = cur;} else {cur.last = tail;tail.next = cur;tail = cur;}}public T popFromHead() {if (head == null) {return null;}Node<T> cur = head;if (head == tail) {head = null;tail = null;} else {head = head.next;cur.next = null;head.last = null;}return cur.value;}public T popFromBottom() {if (head == null) {return null;}Node<T> cur = tail;if (head == tail) {head = null;tail = null;} else {tail = tail.last;tail.next = null;cur.last = null;}return cur.value;}public boolean isEmpty() {return head == null;}}public static class MyStack<T> {private DoubleEndsQueue<T> queue;public MyStack() {queue = new DoubleEndsQueue<T>();}public void push(T value) {queue.addFromHead(value);}public T pop() {return queue.popFromHead();}public boolean isEmpty() {return queue.isEmpty();}}public static class MyQueue<T> {private DoubleEndsQueue<T> queue;public MyQueue() {queue = new DoubleEndsQueue<T>();}public void push(T value) {queue.addFromHead(value);}public T poll() {return queue.popFromBottom();}public boolean isEmpty() {return queue.isEmpty();}}
}

数组实现队列

public class Code04_RingArray {public static class MyQueue {private int[] arr;private int pushi;// endprivate int polli;// beginprivate int size;private final int limit;public MyQueue(int limit) {arr = new int[limit];pushi = 0;polli = 0;size = 0;this.limit = limit;}public void push(int value) {if (size == limit) {throw new RuntimeException("队列满了，不能再加了");}size++;arr[pushi] = value;pushi = nextIndex(pushi);}public int pop() {if (size == 0) {throw new RuntimeException("队列空了，不能再拿了");}size--;int ans = arr[polli];polli = nextIndex(polli);return ans;}public boolean isEmpty() {return size == 0;}// 如果现在的下标是i，返回下一个位置private int nextIndex(int i) {return i < limit - 1 ? i + 1 : 0;}}}

获取栈的最小值

public class Code05_GetMinStack {public static class MyStack1 {private Stack<Integer> stackData;private Stack<Integer> stackMin;public MyStack1() {this.stackData = new Stack<Integer>();this.stackMin = new Stack<Integer>();}public void push(int newNum) {if (this.stackMin.isEmpty()) {this.stackMin.push(newNum);} else if (newNum <= this.getmin()) {this.stackMin.push(newNum);}this.stackData.push(newNum);}public int pop() {if (this.stackData.isEmpty()) {throw new RuntimeException("Your stack is empty.");}int value = this.stackData.pop();if (value == this.getmin()) {this.stackMin.pop();}return value;}public int getmin() {if (this.stackMin.isEmpty()) {throw new RuntimeException("Your stack is empty.");}return this.stackMin.peek();}}public static class MyStack2 {private Stack<Integer> stackData;private Stack<Integer> stackMin;public MyStack2() {this.stackData = new Stack<Integer>();this.stackMin = new Stack<Integer>();}public void push(int newNum) {if (this.stackMin.isEmpty()) {this.stackMin.push(newNum);} else if (newNum < this.getmin()) {this.stackMin.push(newNum);} else {int newMin = this.stackMin.peek();this.stackMin.push(newMin);}this.stackData.push(newNum);}public int pop() {if (this.stackData.isEmpty()) {throw new RuntimeException("Your stack is empty.");}this.stackMin.pop();return this.stackData.pop();}public int getmin() {if (this.stackMin.isEmpty()) {throw new RuntimeException("Your stack is empty.");}return this.stackMin.peek();}}

用两个栈实现一个队列

public class Code06_TwoStacksImplementQueue {public static class TwoStacksQueue {public Stack<Integer> stackPush;public Stack<Integer> stackPop;public TwoStacksQueue() {stackPush = new Stack<Integer>();stackPop = new Stack<Integer>();}// push栈向pop栈倒入数据private void pushToPop() {if (stackPop.empty()) {while (!stackPush.empty()) {stackPop.push(stackPush.pop());}}}public void add(int pushInt) {stackPush.push(pushInt);pushToPop();}public int poll() {if (stackPop.empty() && stackPush.empty()) {throw new RuntimeException("Queue is empty!");}pushToPop();return stackPop.pop();}public int peek() {if (stackPop.empty() && stackPush.empty()) {throw new RuntimeException("Queue is empty!");}pushToPop();return stackPop.peek();}}
}

用两个队列实现一个栈

public class Code07_TwoQueueImplementStack {public static class TwoQueueStack<T> {public Queue<T> queue;public Queue<T> help;public TwoQueueStack() {queue = new LinkedList<>();help = new LinkedList<>();}public void push(T value) {queue.offer(value);}public T poll() {while (queue.size() > 1) {help.offer(queue.poll());}T ans = queue.poll();Queue<T> tmp = queue;queue = help;help = tmp;return ans;}public T peek() {while (queue.size() > 1) {help.offer(queue.poll());}T ans = queue.poll();help.offer(ans);Queue<T> tmp = queue;queue = help;help = tmp;return ans;}public boolean isEmpty() {return queue.isEmpty();}}
}

递归

用递归求数组求arr中的最大值

public class Code08_GetMax {// 求arr中的最大值public static int getMax(int[] arr) {return process(arr, 0, arr.length - 1);}// arr[L..R]范围上求最大值  L ... R   Npublic static int process(int[] arr, int L, int R) {// arr[L..R]范围上只有一个数，直接返回，base caseif (L == R) { return arr[L];}// L...R 不只一个数// mid = (L + R) / 2int mid = L + ((R - L) >> 1); // 中点   	1int leftMax = process(arr, L, mid);int rightMax = process(arr, mid + 1, R);return Math.max(leftMax, rightMax);}}