Sorting and Searching

1
Sorting and Searching

• Often with arrays it's more useful to return the
  index of an array element, rather than the
  elements value.

• Ex if string name is an array of names of
  contest participants, and int score is an array
  of scores, such that participant namei has
  score scorei,
• then knowing the value of the largest element in
  score won't tell who the winner is, but knowing
  the index of the largest element in score will.

• int maxIndex(int A, int N)
• int iMax 0
• for(int i 1 i lt N i)
• if (AiMax lt Ai)
• imax i
• return imax

2
Sorting using Selection Sort

• Selection Sort is so named because it selects the
  largest of the remaining elements and puts it in
  its proper spot in the sorted array.
• void selectionSort(int A, int N)
• for(int length N length gt 1
• length--)
• int k maxIndex(A,length)
• int temp Alength-1
• Alength-1 Ak
• Ak temp
• // end for
• // end selectionSort

• 1st swap the largest element in the array with
  the last element of the array,
• Then ignore the last array slot and move on to
  the largest element in the remainder of the array
  

int maxIndex(int A, int N) int iMax 0
for(int i 1 i lt N i) if (AiMax lt
Ai) imax i return imax // end
maxIndex
3
Searching

• Consider searching for value x in an array A of N
  elements, and return the index of an element of A
  that matches the value x.
• If no such element is found, an index of N is
  returned and, since it is not a valid index, the
  caller of the function can take to mean that no
  match was found.
• For example, to search in an array of objects of
  type string, we can define the following
  function

• int search(string A, int N, string x)
• int i 0
• while(i lt N Ai ! x)
• i
• return i / returns N or the index of the
  cell holding the value /
• We might need to use a function match instead of
  to determine whether two objects match
• int search(string A, int N, string x)
• int i 0
• while(i lt N !match(Ai,x))
• i // need to define match()
• return i

4
ICE Sorting by last, then first, name

• Write a program that reads in a list of 10 names
  (first name followed by last name) and prints
  them out in the usual order - i.e. alphabetically
  by last name, using first names to break ties.

input Tina Tomalito John Maynor Dave Smith Bill
Smith Andy Ahern
output Ahern, Andy Maynor, John Smith, Bill
Smith, Dave Tomalito, Tina