137 lines
3.0 KiB
Java
137 lines
3.0 KiB
Java
package Stack;
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import java.util.Iterator;
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/**
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* 顺序栈的动态扩容
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* Author: PeiJiaNi
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* @param <T> 顺序栈元素类型
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*/
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public class DynamicStackBaseArray<T> implements Iterable<T> {
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private T[] items; // 数组
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private int count; // 栈中的元素个数
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private int length; // 栈空间大小
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/**
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* 初始化栈
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*
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* @param length 栈空间大小
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*/
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public DynamicStackBaseArray(int length) {
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this.items = (T[]) new Object[length];
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this.count = 0;
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this.length = length;
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}
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/**
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* 入栈操作 平均时间复杂度O(1)
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*
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* @param item 入栈元素
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*/
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public void push(T item) {
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// 栈空间已满，则扩容
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if (count == length) {
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resize(2 * items.length);
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}
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items[count++] = item;
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}
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/**
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* 出栈操作 平均时间复杂度O(1)
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*
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* @return 如果栈内不为空，则返回栈顶元素，否则返回-1
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*/
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public T pop() {
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if (count == 0) {
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System.out.println("当前栈已空，无法进行出栈操作");
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return null;
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}
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T item = items[--count];
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items[count] = null;
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if (count > 0 && (count == items.length / 4)) {
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resize(items.length / 2);
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}
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// 返回下标为 count-1 的数组元素，并且栈中元素个数count-1
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return item;
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}
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/**
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* 栈空间动态增加或减小
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*
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* @param size
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*/
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private void resize(int size) {
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T[] newItems = (T[]) new Object[size];
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for (int i = 0; i < count; i++) {
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newItems[i] = this.items[i];
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}
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this.items = newItems;
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}
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//返回栈中最近添加的元素而不删除它
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public T peek() {
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return items[count - 1];
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}
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/**
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* 判断当前栈是否为空
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*
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* @return 栈为空，则返回true,否则返回-1
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*/
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public boolean isEmpty() {
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return count == 0;
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}
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/**
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* 返回栈中元素个数
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*
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* @return
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*/
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public int size() {
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return count;
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}
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@Override
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public Iterator<T> iterator() {
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return new ArrayIterator();
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}
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// 内部类
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class ArrayIterator implements Iterator {
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int numOfItems = count;
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@Override
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public boolean hasNext() {
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return numOfItems > 0;
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}
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@Override
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public T next() {
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return items[--numOfItems];
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}
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}
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public static void main(String[] args) {
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DynamicStackBaseArray<Integer> stack = new DynamicStackBaseArray<Integer>(6);
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stack.push(1);
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stack.push(2);
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stack.push(3);
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stack.push(4);
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stack.push(5);
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// System.out.println(stack.peek());
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Iterator iterator = stack.iterator();
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// System.out.println(iterator.hasNext());
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while (iterator.hasNext()) {
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System.out.println(iterator.next());
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}
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}
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}
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