java/lists/linked-lists/README.md

Lists

Abstract List Type

The list abstract data type (ADT) implements the following methods:

• size
• isEmpty
• first
• last
• addFirst
• addLast
• removeFirst

Other convenience methods:

• remove
• removeFirst
• removeLast
• removeElement

Mistakes Learnings Tricks

Use the Integer class when processing integers!

When you have a String and you want an integer:

• Integer.parse(“525”)

When you have an integer and you want a String:

• Integer.toString(str)

In general, you can also use the String class to turn the object into a String:

• String.valueOf(o)

Linked List specific details:

• Need to handle cases where you are adding to an empty list, or removing last item from list
• Especially when using tail pointer, be aware of what it is pointing to and when it needs to be updated.

Linked list methods should automatically become a list of bookkeeping things to do.

• Add method: consider adding to an empty list, non-empty list
• Add at index i:
  • What are all possible cases?
  • i is too big, i is too small
  • the list is empty
  • i is a special case
  • how can we fold any of these cases into other cases (list empty -> i too small)

Size of linked list:;

• Number of bytes:
  • See https://charlesreid1.com/wiki/Java/Memory
  • 8 bytes per reference to memory (64 bit)
  • 16 bytes of object overhead
• Size estimation:
  • 1000-integer linked list should theoretically use up:
  • 1000 nodes x ( 4 bytes per integer + 8 bytes per ref + 16 bytes object overhead )
  • 28,0000 bytes ~ 28 kB
  • What’s the power of 2 that would correspond to that?
  • 1000 integers ~ 1024 integers ~ 2^10 integers
  • Round it up to 8 bytes per integer, 8 bytes per ref, 16 bytes per object overhead)
  • 2^5 = 32 bytes per integer
  • 32 x 8 = 2^5 * 2^3 = 2^8 = 256 bits = 256 zeroes and ones
  • 10 GB / 10 kB/obj = 10x10^6 / 10 = 10^6

Exceptions:

class Empty extends Exception{};

Circular linked list:

• Take care with the details of pointers.

Doubly linked list:

• It makes algorithms easier, but

Nice link explaining sizes of Strings in memory:

• https://stackoverflow.com/a/18030595

sizeof(string) =
8 + // object header used by the VM
8 + // 64-bit reference to char array (value)
8 + string.length() * 2 + // character array itself (object header + 16-bit chars)
4 + // offset integer
4 + // count integer
4 + // cached hash code

Timing:

• Don’t do logarithmic size.........
• Need to fix that actually.
• Cover a single order of magnitude, then maybe try for two.