返回仅包含奇数整数的数组

Question

Ok, so I have this problem where when given an Array arr, return an Array which contains only odd integers in the original order from arr.

My code:

public int [] youMakeMeOdd(int [] arr)
{
   int[] odds;
   odds = new int[arr.length];
   for(int i = 0; i < arr.length; i++)
   {
      if(arr[i] % 2 != 0)
      {
         odds[i] = arr[i];
      }
   }
   return odds;
}

Few Testers:

Expected...........................................................Run:

youMakeMeOdd({1,2,3}) → {1, 3}.....................{1, 0, 3}

youMakeMeOdd({2,1,3,5,7}) → {1, 3, 5, 7}.......{0, 1, 3, 5, 7}

youMakeMeOdd({2,4,6,8}) → {}........................{0, 0, 0, 0}

.

I can't seem to figure out how to put a blank space there instead of 0's. Help appreciated, thanks :)

Answer 1

The output array is being initialized to the size of the input array. I guess this being java code, the array elements are initialized to zero by default. So whenever the if condition does skips the ith position the default value (zero) is being shown.

public int[] youMakeMeOdd(int [] arr) {
   List<Integer> odds = new ArrayList<Integer>();
   for(int i = 0; i < arr.length; i++)
   {
      if(arr[i] % 2 != 0)
      {
         odds.add(arr[i]);
      }
   }
   return convertIntegers(odds);
}

public static int[] convertIntegers(List<Integer> integers)
{
    int[] ret = new int[integers.size()];
    Iterator<Integer> iterator = integers.iterator();
    for (int i = 0; i < ret.length; i++)
    {
        ret[i] = iterator.next().intValue();
    }
    return ret;
}

Answer 2

You could have a pre-computation loop where you just increment a counter and then allocate odds:

int counter = 0;
for (int i = 0; i < arr.length; i++)
{
    if (arr[i] % 2 != 0)
    {
        counter ++;
    }
}
odds = new int[counter];

Answer 3

var result = input.Select(a=>a % 2 != 0 ? a : 0).ToArray()

您可以轻松地使用linq ，基本上是使用原始数组，然后使用Select选择数组本身的值或选择0（如果它是偶数），然后使用ToArray方法转换为array 。

Answer 4

I would use an ArrayList. Your problems seems to be the fact that arrays are immutable, so you it automatically fills your array with a bunch of unneeded 0s. ArrayLists can change dimensions, so you don't have to have the 0s.

You can have a look at them here: http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html

Make sure you import the util package.

 import java.util.*;



public ArrayList<Integer>  youMakeMeOdd(int [] arr)
{

You need to specify the type that you want to hold in the angle braces. Because int is a primitive, you need to use the Integer class

   ArrayList<Integer> odds;
   odds = new ArrayList<>();
   for(int i = 0; i < arr.length; i++)
   {
      if(arr[i] % 2 != 0)
      {

The add method adds an integer to the end

         odds.add(new Integer(arr[i]));
      }
   }
   return odds;
}