Tres, cola
1. Concepto
La cola es una FIFOestructura de datos de recopilación que sigue (primero en entrar, primero en salir), es decir, el elemento que se coloca primero en la cola es también el primero en obtenerse
Su capa inferior se puede implementar con una matriz o una lista vinculada. Tiene 2 punteros, que apuntan al nodo de la cabeza y al nodo de la cola respectivamente. Al agregar un elemento, mueve el nodo de la cola hacia atrás, y al quitar un elemento, mueve el nodo de la cabeza hacia atrás.
2. Métodos comunes
- poner agrega elementos a la cola
- tomar elimina el primer elemento de la cola (mueve el nodo principal hacia atrás)
- peek saca el primer elemento de la cola (no mueva el nodo principal)
3. Ejemplo
1) cola de matriz
class ArrayQueue<T> {
private final int length;
private Object[] array;
private int head; // 指向本次要移出的元素的前一个位置
private int tail; // 指向本次要添加的元素的前一个位置
public ArrayQueue(int length) {
this.length = length;
this.array = new Object[this.length];
this.head = -1;
this.tail = -1;
}
public void put(T element) {
if (isFull()) {
return;
}
this.tail++;
array[tail] = element;
}
public T take() {
if (isEmpty()) {
return null;
}
this.head++;
@SuppressWarnings("unchecked")
T element = (T)array[head];
if (head == tail) {
head = -1;
tail = -1;
}
return element;
}
@SuppressWarnings("unchecked")
public T peek() {
if (isEmpty()) {
return null;
}
return (T)array[head + 1];
}
public int size() {
return tail - head;
}
@Override
public String toString() {
if (isEmpty()) {
return "[]";
}
StringBuilder sBuilder = new StringBuilder("[");
for (int i = head + 1, size = i + size(); i < size; i++) {
sBuilder.append(array[i]);
if (i != size - 1) {
sBuilder.append(", ");
} else {
sBuilder.append("]");
}
}
return sBuilder.toString();
}
public boolean isFull() {
return tail == length - 1;
}
public boolean isEmpty() {
return -1 == head && head == tail;
}
}
2) Cola de lista vinculada
class LinkedQueue<T> {
private final int length;
private Node<T> head; // 头节点指向本次可以取出的节点
private Node<T> tail; // 尾节点指向最后一个节点
private int size;
public LinkedQueue(int length) {
this.length = length;
this.head = null;
this.tail = null;
this.size = 0;
}
public void put(T element) {
if (isFull()) {
return;
}
Node<T> add = new Node<T>(element);
if (null == head) {
this.head = add;
}
if (null != tail) {
tail.next = add;
}
this.tail = add;
this.size++;
}
public T take() {
if (isEmpty()) {
return null;
}
T element = head.element;
if (head == tail) {
// 最后一个元素，将尾节点也置为空
this.tail = null;
}
this.head = head.next;
this.size--;
return element;
}
public T peek() {
if (isEmpty()) {
return null;
}
return head.element;
}
public int size() {
return size;
}
@Override
public String toString() {
if (isEmpty()) {
return "[]";
}
StringBuilder sBuilder = new StringBuilder("[");
Node<T> node = this.head;
while (true) {
sBuilder.append(node.element);
if (null == node.next) {
break;
}
sBuilder.append(", ");
node = node.next;
}
sBuilder.append("]");
return sBuilder.toString();
}
public boolean isFull() {
return size == length;
}
public boolean isEmpty() {
return 0 == size;
}
private static class Node<T> {
private final T element;
private Node<T> next;
private Node(T element) {
this.element = element;
}
@Override
public String toString() {
return (null != element) ? element.toString() : "null";
}
}
}
3) Cola circular
class CircleQueue<T> {
private final int length;
private Object[] array;
private int head; // 指向队头
private int tail; // 指向队尾
public CircleQueue(int length) {
this.length = length + 1; // 多出一个位置，用于存放上一次取出的元素。更新指针时访问不到它
this.array = new Object[this.length];
this.head = 0;
this.tail = 0;
}
public void put(T element) {
if (isFull()) {
return;
}
array[tail] = element;
tail = (tail + 1) % length;
}
public T take() {
if (isEmpty()) {
return null;
}
@SuppressWarnings("unchecked")
T element = (T)array[head];
head = (head + 1) % length;
return element;
}
@SuppressWarnings("unchecked")
public T peek() {
if (isEmpty()) {
return null;
}
return (T)array[head];
}
public int size() {
return (tail + length - head) % length;
}
public boolean isFull() {
return (tail + 1) % length == head;
}
public boolean isEmpty() {
return head == tail;
}
@Override
public String toString() {
if (isEmpty()) {
return "[]";
}
StringBuilder sBuilder = new StringBuilder("[");
for (int i = head, size = i + size(); i < size; i++) {
sBuilder.append(array[i % length]);
if (i != size - 1) {
sBuilder.append(',').append(' ');
}
}
sBuilder.append(']');
return sBuilder.toString();
}
}