• Understand the definition of the brute force design pattern.
• Describe several algorithms that are classified as brute force design.
• Discuss the strengths and weaknesses of brute force design.

Intro

• You should read chapter 3.
• We will begin to study design approaches.
  • How can we solve problems?
  • How can we design algorithms for our solution?
• Brute force design is a is a straight forward approach to solving a problem, usually directly based on the problem statement and definitions of the concepts involved. (From the book)
• The author classifies Selection Sort as a brute force sort.
• And the string match we saw in chapter 1.
• And the algorithms Dr. Meyer presented as well.
• Brute force design
  • Is usually not the most efficient solution.
  • The design methodology can be applied to almost every problem.
  • But is sometimes "good enough".
  • It can provide insight into the problem
    • Analyzing brute force solutions can help us understand the problem better.
    • And can help us understand what is expensive in the brute force solution
    • And can provide a base line check for other algorithms.

Bubble Sort

• A brute force sort.

• BUBBLE_SORT(A)
  
   for i ← 0  to  n-2 do
       for j ← 0 to n-2-i do
           if A[j+1] > A[j] then
              swap(A[j+1],A[j])
   return
  
     

• Questions?
• Trace with 8 2 4 1 9 3
• Can we do better?
• Notice
  • After the last swap occurs, the remainder of the array is in order
  • If no swaps occur, then the array is in order.
  • If either of these conditions are met, we can stop early.

  • BETTER_BUBBLE(A)
    
     n ← A.size()-1
     while n > 0  do
        newN ← 0
        for i ← 0 to n-1  do
               if A[j+1] > A[j] then
                   swap(A[j+1],A[j])
                   newN ← i
        n ← newN
     return
    
    	

  • Same questions, but IS IT BETTER?
• Bubble Sort can be effective if there are a few items, just one place out of order.
• Is bubble sort stable?
• Is it in place?