Design and Analysis Bubble Sort


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Bubble Sort is an elementary sorting algorithm, which works by repeatedly exchanging adjacent elements, if necessary. When no exchanges are required, the file is sorted.

This is the simplest technique among all sorting algorithms.

Algorithm: Sequential-Bubble-Sort (A) 
fori← 1 to length [A] do 
for j ← length [A] down-to i +1 do 
   if A[A] < A[j - 1] then 
      Exchange A[j] ↔ A[j-1] 

Implementation

voidbubbleSort(int numbers[], intarray_size) { 
   inti, j, temp; 
   for (i = (array_size - 1); i >= 0; i--) 
   for (j = 1; j <= i; j++) 
      if (numbers[j - 1] > numbers[j]) { 
         temp = numbers[j-1]; 
         numbers[j - 1] = numbers[j]; 
         numbers[j] = temp; 
      } 
} 

Analysis

Here, the number of comparisons are

1 + 2 + 3 +...+ (n - 1) = n(n - 1)/2 = O(n2)

Clearly, the graph shows the n2 nature of the bubble sort.

In this algorithm, the number of comparison is irrespective of the data set, i.e. whether the provided input elements are in sorted order or in reverse order or at random.

Memory Requirement

From the algorithm stated above, it is clear that bubble sort does not require extra memory.

Example

Unsorted list:

5 2 1 4 3 7 6

1st iteration:

5 > 2 swap

2 5 1 4 3 7 6

5 > 1 swap

2 1 5 4 3 7 6

5 > 4 swap

2 1 4 5 3 7 6

5 > 3 swap

2 1 4 3 5 7 6

5 < 7 no swap

2 1 4 3 5 7 6

7 > 6 swap

2 1 4 3 5 6 7

2nd iteration:

2 > 1 swap

1 2 4 3 5 6 7

2 < 4 no swap

1 2 4 3 5 6 7

4 > 3 swap

1 2 3 4 5 6 7

4 < 5 no swap

1 2 3 4 5 6 7

5 < 6 no swap

1 2 3 4 5 6 7

There is no change in 3rd, 4th, 5th and 6th iteration.

Finally,

the sorted list is

1 2 3 4 5 6 7
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