为算法考试做准备--ArrayList实现

最新推荐文章于 2022-10-05 10:52:17 发布

原创最新推荐文章于 2022-10-05 10:52:17 发布 · 556 阅读

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#数据结构 #算法 #ArrayList

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本文主要探讨了为算法考试准备过程中ArrayList数据结构的重要性，详细解析了ArrayList的内部实现，包括其添加、删除、查找等操作的时间复杂度分析，旨在帮助考生更好地理解和运用ArrayList解决算法问题。

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package utils;

public class MyArrayList<T> {
	private static final int DEFAULT_CAPACITY = 50;
	private int theSize;
	private Object[] theItems;
	
	public MyArrayList() {
		clear();
	}
	
	public void clear() {
		theSize = 0;
		ensureCapacity(DEFAULT_CAPACITY);
	}
	
	public int size() {
		return theSize;
	}
	
	public boolean isEmpty() {
		return size() == 0;
	}
	
	public void trimToSize() {
		ensureCapacity(size());
	}
	
	public T get(int idx) {
		if (idx < 0 || idx >= size())
			return null;// should throw exception
		return (T)theItems[idx];
	}
	
	public T get(T x) {
		for (int i = 0; i < size(); ++i) {
			if (theItems[i].equals(x)) {
				return (T)theItems[i];
			}
		}
		return null;
	}
	
	public int indexOf(T x) {
		for (int i = 0; i < size(); ++i) {
			if (theItems[i].equals(x)) {
				return i;
			}
		}
		return -1;
	}
	
	public T set(int idx, T newVal) {
		if (idx < 0 || idx >= size())
			return null;
		T old = (T)theItems[idx];
		theItems[idx] = newVal;
		return old;
	}
	
	public void ensureCapacity(int newCapacity) {
		if (newCapacity < theSize)
			return;
		Object[] old = theItems;
		theItems = new Object[newCapacity];
		for (int i = 0; i < size(); ++i)
			theItems[i] = old[i];
	}
	
	public boolean add(T x) {
		add(size(), x);
		return true;
	}
	
	public void add(int idx, T x) {
		if (theItems.length == size())
			ensureCapacity(size() * 2 + 1);
		for (int i = theSize; i > idx; i--)
			theItems[i] = theItems[i - 1];
		theItems[idx] = x;
		theSize++;
	}
	
	public T remove(int idx) {
		T removedItem = (T)theItems[idx];
		for (int i = idx; i < size() - 1; ++i)
			theItems[i] = theItems[i+1];
		theItems[size() - 1] = null;
		theSize--;
		return removedItem;
	}
	
	public T remove(T x) {
		for (int i = 0; i < size(); ++i) {
			if (theItems[i].equals(x)) {
				return remove(i); 
			}
		}
		return null;
	}
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] a = new int[] {2, 8, 3, 4, 9, 10};
		MyArrayList<Integer> list = new MyArrayList<Integer>();
		for (int i : a) {
			list.add(i);
		}
		for (int i = 0; i < list.size(); ++i) {
			System.out.print(list.get(i) +" ");
		}
		System.out.println();
		System.out.println(list.remove((Integer)2));
		System.out.println(list.remove((Integer)10));
		System.out.println(list.remove((Integer)3));
		System.out.println(list.add((Integer)3));
		for (int i = 0; i < list.size(); ++i) {
			System.out.print(list.get(i) +" ");
		}
	}

}