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Re-order array putting zeros at the end of c #

I am trying to do LRU and keep track of the order of the values.

So, let's say I have an array items = "P1", "P3", null, null

  • P4 appears (items = "P1", "P3", "P4", null

    )
  • P4 doesn't exist yet, so I just add it to the smallest index null

    .
  • But then P1 reappears, so point P1 goes to null

    (items = null, "P3", "P4", null

    )
  • I need a way ( my question ) to offset everything like this (items = "P3", "P4", null, null

    )
  • Then add P1 to the lowest index null

    (items = "P3", "P4", "P1", null

    )
  • And so on, LRU tracking

So I need to find a way to move all non-null elements to the beginning of the array (in order).

I found a post that used this items = items.Where(s => !String.IsNullOrEmpty(s)).ToArray();

one however this removes all null

s when I want to keep the array size intact.

How can I keep the size of the array by moving all zeros to the end and all nonzeros to the front (keeping all values ​​in order)

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2 answers


Just literally "Non-zero elements first, then zero elements":

var nulls = items.Where(x => x == null);
var nonnulls = items.Where(x => x != null);
var result = nonnulls.Concat(nulls);


Or:

var result = items.OrderBy(x => x == null).ThenBy(x => x.SomeOtherKey);
+4


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Here is a solution that doesn't create a new array. It just rebuilds the existing array.

static void MoveFront<T>(T[] arr) where T : class
{
    int ileft = 0;
    int iright = 1;

    while (iright < arr.Length)
    {
        T left = arr[ileft];
        T right = arr[iright];

        if (left == null && right != null)
        {
            Swap(arr, ileft++, iright++);
        }
        else if (left == null && right == null)
        {
            iright++;
        }
        else if (left != null && right != null)
        {
            ileft += 2;
            iright += 2;
        }
        else if (left != null && right == null)
        {
            ileft++;
            iright++;
        }
    }
}

static void Swap<T>(T[] arr, int left, int right)
{
    T temp = arr[left];
    arr[left] = arr[right];
    arr[right] = temp;
}


Name it like this:

string[] arr = { "a", null, "b", null, "c" };
MoveFront(arr);
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