我制作了一个程序,它采用arraylist中的元素列表并使用递归,获取偶数和奇数元素。例如,如果它是{1,2,3,4,5,6}。它将返回{1,3,5},因为它们具有偶数元素放置。
我想出了如何顺利地为偶数做到这一点,但我似乎无法让它适用于赔率。
以下是错误:
java.lang.ArrayIndexOutofBoundsException:
-1 (in java.util.ArrayList)
这是我的偶数代码:
public static ArrayList<Integer> even(ArrayList<Integer> tList)
{
ArrayList<Integer> newList = ListMethods.deepClone(tList);
int temp = newList.size();
if (newList.size()<=0)// The list is empty or has one element)
{
return newList;// Return the list as is – no need to reverse!
}
else
{
if(newList.size()%2==0)
temp = newList.remove(newList.size()-2);
newList.remove(newList.size()-1);
newList = ListMethods.even(newList);
if (temp!=0)
newList.add(temp);
}
return newList;
}
奇数代码:(这是我收到错误的地方)
public static ArrayList<Integer> odd(ArrayList<Integer> tList)
{
ArrayList<Integer> newList = ListMethods.deepClone(tList);
int temp = newList.size();
if (newList.size()<=0)// The list is empty or has one element)
{
return newList;// Return the list as is – no need to reverse!
}
else
{
if(newList.size()%2==1)
temp = newList.remove(newList.size()-1);
newList.remove(newList.size()-1);
newList = ListMethods.odd(newList);
if (temp!=0)
newList.add(temp);
}
return newList;
}
深度克隆:
public static ArrayList<Integer> deepClone(ArrayList<Integer> tList)
{
ArrayList<Integer> list = new ArrayList<Integer>();
for (Integer i : tList)
{
list.add(new Integer(i));
}
return list;
}
我的测试人员代码:
import java.util.ArrayList;
import java.util.Scanner;
public class ListMethodsRunner
{
public static void main(String[] args)
{
ArrayList<Integer> tempList = ListMethods.makeList(100);
System.out.println("What would you like to do to this ArrayList? Type the number.");
System.out.println("1. Show Even Elements");
System.out.println("2. Show Odd Elements");
System.out.println(" ");
Scanner input = new Scanner(System.in);
int z = input.nextInt();
if(z==1)
tempList = ListMethods.even(tempList);
if(z==2)
tempList = ListMethods.odd(tempList);
if (tempList.size() == 0)
{
System.out.println("The list is empty");
}
else
{
for (Integer i : tempList)
{
System.out.println(i);
}
}
}
}
答案 0 :(得分:0)
没关系,我自己想出来了。
public static ArrayList<Integer> odd(ArrayList<Integer> tList)
{
ArrayList<Integer> newList = ListMethods.deepClone(tList);
int temp = newList.size();
if (newList.size()<=0)// The list is empty or has one element)
{
return newList;// Return the list as is – no need to reverse!
}
else
{
if(newList.size()%2==0) // I had `1` here instead of `0`
temp = newList.remove(newList.size()-1);
newList.remove(newList.size()-1);
newList = ListMethods.odd(newList);
if (temp!=0)
newList.add(temp);
}
return newList;
答案 1 :(得分:0)
我不确定上面的代码是否有用,以防您有奇数条目可能您可以使用以下内容:
public static ArrayList<Integer> returnList(ArrayList<Integer> tList,boolean flag){
int size=tList.size();
int t;
//print odd positions - flag is true
if(flag){
if(size>0 && size%2==0){
t = tList.remove(size-1);
tList=returnList(tList,flag);
tList.add(t);
}
else if(size%2 == 1){
t = tList.remove(size-1);
tList=returnList(tList,flag);
}
else{
}
System.out.println("Printing.."+tList);
}
else{
}
return tList;
}