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Bubble sort

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Bubble sort

  1. 1. Sorting • Sorting takes an unordered collection and makes it an ordered one. 512354277 101 1 2 3 4 5 6 5 12 35 42 77 101 1 2 3 4 5 6
  2. 2. Exchange/Bubble Sort: It uses simple algorithm. It sorts by comparing each pair of adjacent items and swapping them in the order. This will be repeated until no swaps are needed. The algorithm got its name from the way smaller elements "bubble" to the top of the list. It is not that much efficient, when a list is having more than a few elements. Among simple sorting algorithms, algorithms like insertion sort are usually considered as more efficient. Bubble sort is little slower compared to other sorting techniques but it is easy because it deals with only two elements at a time.
  3. 3. "Bubbling Up" the Largest Element • Traverse a collection of elements – Move from the front to the end – “Bubble” the largest value to the end using pair-wise comparisons and swapping 512354277 101 1 2 3 4 5 6
  4. 4. "Bubbling Up" the Largest Element • Traverse a collection of elements – Move from the front to the end – “Bubble” the largest value to the end using pair-wise comparisons and swapping 512354277 101 1 2 3 4 5 6 Swap42 77
  5. 5. "Bubbling Up" the Largest Element • Traverse a collection of elements – Move from the front to the end – “Bubble” the largest value to the end using pair-wise comparisons and swapping 512357742 101 1 2 3 4 5 6 Swap35 77
  6. 6. "Bubbling Up" the Largest Element • Traverse a collection of elements – Move from the front to the end – “Bubble” the largest value to the end using pair-wise comparisons and swapping 512773542 101 1 2 3 4 5 6 Swap12 77
  7. 7. "Bubbling Up" the Largest Element • Traverse a collection of elements – Move from the front to the end – “Bubble” the largest value to the end using pair-wise comparisons and swapping 577123542 101 1 2 3 4 5 6 No need to swap
  8. 8. "Bubbling Up" the Largest Element • Traverse a collection of elements – Move from the front to the end – “Bubble” the largest value to the end using pair-wise comparisons and swapping 577123542 101 1 2 3 4 5 6 Swap5 101
  9. 9. "Bubbling Up" the Largest Element • Traverse a collection of elements – Move from the front to the end – “Bubble” the largest value to the end using pair-wise comparisons and swapping 77123542 5 1 2 3 4 5 6 101 Largest value correctly placed
  10. 10. Bubble Sort 1. In each pass, we compare adjacent elements and swap them if they are out of order until the end of the list. By doing so, the 1st pass ends up “bubbling up” the largest element to the last position on the list 2. The 2nd pass bubbles up the 2nd largest, and so on until, after N-1 passes, the list is sorted. Example: Pass 1 89 | 45 68 90 29 34 17 Pass 2 45 | 68 89 29 34 17 45 89 | 68 90 29 34 17 45 68 | 89 29 34 17 68 89 | 90 29 34 17 68 89 | 29 34 17 89 90 | 29 34 17 29 89 | 34 17 29 90 | 34 17 34 89 | 17 34 90 | 17 17 89 17 90 45 68 89 29 34 17 90 45 68 29 34 17 89 largest 2nd largest
  11. 11. The “Bubble Up” Algorithm index <- 1 last_compare_at <- n – 1 loop exitif(index > last_compare_at) if(A[index] > A[index + 1]) then Swap(A[index], A[index + 1]) endif index <- index + 1 endloop
  12. 12. No, Swap isn’t built in. Procedure Swap(a, b isoftype in/out Num) t isoftype Num t <- a a <- b b <- t endprocedure // Swap LB
  13. 13. Items of Interest • Notice that only the largest value is correctly placed • All other values are still out of order • So we need to repeat this process 77123542 5 1 2 3 4 5 6 101 Largest value correctly placed
  14. 14. Repeat “Bubble Up” How Many Times? • If we have N elements… • And if each time we bubble an element, we place it in its correct location… • Then we repeat the “bubble up” process N – 1 times. • This guarantees we’ll correctly place all N elements.
  15. 15. “Bubbling” All the Elements 77123542 5 1 2 3 4 5 6 101 5421235 77 1 2 3 4 5 6 101 4253512 77 1 2 3 4 5 6 101 4235512 77 1 2 3 4 5 6 101 4235125 77 1 2 3 4 5 6 101 N-1
  16. 16. Reducing the Number of Comparisons 12354277 101 1 2 3 4 5 6 5 77123542 5 1 2 3 4 5 6 101 5421235 77 1 2 3 4 5 6 101 4253512 77 1 2 3 4 5 6 101 4235512 77 1 2 3 4 5 6 101
  17. 17. Reducing the Number of Comparisons • On the Nth “bubble up”, we only need to do MAX-N comparisons. • For example: – This is the 4th “bubble up” – MAX is 6 – Thus we have 2 comparisons to do 4253512 77 1 2 3 4 5 6 101
  18. 18. Putting It All Together
  19. 19. N is … // Size of Array Arr_Type definesa Array[1..N] of Num Procedure Swap(n1, n2 isoftype in/out Num) temp isoftype Num temp <- n1 n1 <- n2 n2 <- temp endprocedure // Swap
  20. 20. procedure Bubblesort(A isoftype in/out Arr_Type) to_do, index isoftype Num to_do <- N – 1 loop exitif(to_do = 0) index <- 1 loop exitif(index > to_do) if(A[index] > A[index + 1]) then Swap(A[index], A[index + 1]) endif index <- index + 1 endloop to_do <- to_do - 1 endloop endprocedure // Bubblesort Innerloop Outerloop
  21. 21. Summary • “Bubble Up” algorithm will move largest value to its correct location (to the right) • Repeat “Bubble Up” until all elements are correctly placed: – Maximum of N-1 times • We reduce the number of elements we compare each time one is correctly placed
  22. 22. Thank You

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