Some Simple Algorithms on Linked Lists

1
Some Simple Algorithms on Linked Lists

• Write a function that returns the length of a
  given list.
• Write a boolean function that tests whether a
  given unsorted list of characters is a
  palindrome.
• Write a function that computes the union of two
  sorted linked lists of integers.

2
The length of a given list

• int length(NodePtr Head)
• int size 0
• NodePtr cur Head
• while(cur ! NULL)
• size
• cur cur-gtnext
• return size

3
It can also be recursive

• int lengthRec(NodePtr Head)
• if(HeadNULL)
• return 0
• return length(Head-gtnext) 1

4
Test if the given list is a palindrome
a b c d d c b a is a palindrome, a b c d c
is not.

• bool isPalindrome(NodePtr head)
• 1. create a new list in inverse order, newList
• 2. check the two lists, head and newList,
  whether they are the same

5
Test if the given list is a palindrome

• bool isPalindrome(NodePtr Head)
• bool result
• // copy the list in reverse order
• NodePtr newList NULL
• NodePtr cur Head
• while(cur ! NULL)
• addHead(newList, cur-gtdata)
• cur cur-gtnext
• // compare the list and reversed list
• result true // assume true
• cur Head
• rev newList
• while(cur!NULL)
• if(cur-gtdata ! rev-gtdata)
• result false // not palindrome!
• cur cur-gtnext
• rev rev-gtnext

6
Union of two sorted lists

• merge(1, 2, 4, 5, 3, 4, 5, 6, 7) gives
• 1, 2, 3, 4, 5, 6, 7
• // returns merged list (changes first list)
• NodePtr merge(NodePtr Head1, NodePtr Head2)
• NodePtr Union, Cur
• if(Head1NULL)
• return Head2
• else if(Head2NULL)
• return Head1
• Union Head1
• Cur Head2
• while(Cur ! NULL)
• if(searchNode(Union, Cur-gtdata)NULL)
• insertNode(Union, Cur-gtdata)
• Cur Cur-gtnext
• return Union