Sorting

• Sorting is the process of putting elements of a list or array in order.
  • Order is somehow defined by a comparison operator.
    • Alphabetic,
    • Numeric
    • Some other order
  • This is done on a key or set of keys
• For now we will sort our words in alphabetic order.
  • The words will be the key
  • string < will be the comparison operator.
• There are a large number of sorting algorithms.
• We will probably discuss two.
  • Selection sort.
  • Insertion sort.
• Selection Sort
  • The big idea is to keep the array divided into two parts
    • A sorted part from 0 to current (left side)
    • An unsorted part from current to size (right side)
  • The big idea:

    • Starting with current at position 0
      while current is not the size of the array
          Find the smallest item in the rest (to the right) of the array.
          Swap the smallest item and the item at  position current
          Increment current
                

  • Try this with

     
    current  search smallest        0   1   2   3   4   5     
                           5   3   4   2   6   1     
    
    
    
    
    
                     

• An algorithm

• Sort(A[], size)
  
   for current ← 0 to size-2
      smallest ← current
      for search ← current+1 to size-1
         if A[smallest] > A[search]
             smallest ← search
      if current ≠ smallest
         swap(A[current], A[smallest])