每日一记--2014.10.11（2）

今天终于进展到了第三章，好好读了读链表

其实对于linkedlist来说，它的remove也会是O(N)，因为对于删除这个动作确实是常数时间的，但是对于定位到被删除元素的位置就需要有线性时间的开销了

今天参照书上的把ArrayList类编了编，定名为MyArrayListM

package myarraylist;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class MyArrayListM<AnyType> implements Iterable<AnyType>{
    private static final int DEFAULT_SIZE=10;
    private int theSize;
    private AnyType[] items;
    
    MyArrayListM(){
        theSize=0;
        ensureCapacity(DEFAULT_SIZE);
    }
    public int size(){
        return theSize;
    }
    public boolean isEmpty(){
        return theSize==0;
    }
    public void trimToSize(){
        ensureCapacity(size());
    }
    public AnyType get(int idx){
        if(idx<0|idx>size())
            throw new ArrayIndexOutOfBoundsException();
        return items[idx];
    }
    public AnyType set(int idx,AnyType element){
        if(idx<0|idx>size())
            throw new ArrayIndexOutOfBoundsException();
        AnyType old = items[idx];
        items[idx]=element;
        return old;
    }
    public void add(AnyType element){
        add(size(),element);
    }
    public void add(int idx,AnyType element){
        if(idx<0|idx>size())
            throw new ArrayIndexOutOfBoundsException();
        if(items.length==size())
            ensureCapacity(size()*2);
        for(int i=size();i>idx;i--){//改变一下i的取值，可以减少使用一个临时的数组
            items[i]=items[i-1];
        }
        items[idx]=element;
        
        theSize++;//嗯嗯，这个忘记了
    }
    
    public AnyType remove(int idx){
        if(idx<0|idx>size())
            throw new ArrayIndexOutOfBoundsException(); 
        AnyType removed =items[idx];
        for(int i=idx;i<size()-1;i++){
            items[i]=items[i+1];
        }
        theSize--;
        return removed;
        
    }
    @SuppressWarnings("unchecked")
    private void ensureCapacity(int cap) {
        if(cap<size())
            return;
        AnyType[] old = items;
        items = (AnyType[]) new Object[cap];
        for(int i=0;i<size();i++){
            items[i]=old[i];
        }
        
    }
    public Iterator<AnyType> iterator(){
        return new ArrayListIterator();
    }
    private class ArrayListIterator implements Iterator<AnyType> {//ArrayListIterator之后不能加<AnyType>,否则报错
        int current =0;
        @Override
        public boolean hasNext() {
            return current <size();
        }

        @Override
        public AnyType next() {
            if(!hasNext())
                throw new NoSuchElementException();
            return items[current++];
        
        }

        @Override
        public void remove() {
            // TODO Auto-generated method stub
            MyArrayListM.this.remove(current--);
        }
        
    }
    

}