Quicksort algorithm
Illustrated walkthrough
Partition function
This function does the most of the heavy lifting,
so we look at it first, then see it in the context of...
[0]

[1]

[2]

[3]

[4]

[5]

12

7

14

9

10

11

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (array...
store
Index

i

begin

12

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (array[i] <...
i

store
Index

0
begin

12

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (array[i]...
i

0

store
Index

0
begin

12

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (array...
i

store
Index

0
0<5
is true

0
begin

12

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++)...
i

store
Index

0
12 <= 11
is false

0
begin

12

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last...
i

store
Index

1

0
begin

12

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (array...
i

store
Index

1
7 <= 11
is true

0
begin

12

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; ...
i

store
Index

1

0
begin

12

Swap

last

7

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
i

store
Index

1

0
begin

7

Swap

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
i

1

store
Index

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
i

store
Index

2

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
i

store
Index

2
2<5
is true

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++...
i

store
Index

2
14 <= 11
is fase

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last...
i

store
Index

3

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
i

store
Index

3

3<5
is true

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i+...
i

store
Index

3

9 <= 11
is true

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last...
Swap
i

store
Index

3

1

begin

7

last

12

14

9

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
Swap
i

store
Index

3

1

begin

7

last

9

14

12

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
i

store
Index

3

2

begin

7

last

9

14

12

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
i

store
Index

4

2

begin

7

last

9

14

12

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
4<5
is true
store
Index

i

4

2

begin

7

last

9

14

12

10

int storeIndex = begin;
for (int i = begin; i < last; i++...
10 <= 11
is true
store
Index

i

4

2

begin

7

last

9

14

12

10

int storeIndex = begin;
for (int i = begin; i < last...
Swap
i

store
Index

4

2

begin

7

last

9

14

12

10

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
Swap
i

store
Index

4

2

begin

7

last

9

10

12

14

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
i

store
Index

4

3

begin

7

last

9

10

12

14

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
i

store
Index

3

begin

7

5

last

9

10

12

14

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
4<5
is false

store
Index

i

3

begin

7

5

last

9

10

12

14

int storeIndex = begin;
for (int i = begin; i < last; i...
Swap
i

store
Index

3

begin

7

5

last

9

10

12

14

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
Swap
i

store
Index

3

begin

7

5

last

9

10

11

14

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if ...
i

store
Index

3

begin

7

5

last

9

10

11

14

int storeIndex = begin;
for (int i = begin; i < last; i++) {
if (arra...
Quicksort algorithm
Now we use Partition in the context of
Quicksort
pivot
Index

[0]

[1]

[2]

[3]

[4]

9

7

5

11

12

[5]

2

[6]

14

[7]

[8]

3

int pivotIndex = 0;
if (begin < last)...
pivot
Index

0
9

7

5

11

12

2

14

3

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(array, start, end)...
0<9
is true
pivot
Index

0
9

7

5

11

12

2

14

3

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(array,...
Partition
0..9
pivot
Index

0
9

7

5

11

12

2

14

3

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(arr...
these are <= 6

these are > 6

pivot
Index

5

2

3

3

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex...
Call Stack #0

pivot
Index

5

2

3

3

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(arr...
pivot
Index
Call Stack #1
Call Stack #0

5

2

3

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex = Par...
pivot
Index

0

5

2

3

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(array, start, end)...
0<2
is true

pivot
Index

0

5

2

3

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(array...
Partition
0..2
pivot
Index

0

5

2

3

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(arr...
pivot
Index

1

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex = Partition(array, start, end)...
Call Stack #1
Call Stack #0

pivot
Index

1

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex =...
Call Stack #2

pivot
Index

Call Stack #1
Call Stack #0

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
...
Call Stack #2
Call Stack #1
Call Stack #0

pivot
Index

0

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) ...
Call Stack #2

0<0
is false

Call Stack #1
Call Stack #0

pivot
Index

0

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if...
Call Stack #2
Call Stack #1
Call Stack #0

pivot
Index

0

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) ...
Call Stack #1
Call Stack #0

pivot
Index

1

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex =...
Call Stack #2

pivot
Index

Call Stack #1
Call Stack #0

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
...
Call Stack #2
Call Stack #1
Call Stack #0

pivot
Index

2

0

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) ...
0<0
is false

Call Stack #2
Call Stack #1
Call Stack #0

pivot
Index

2

0

3

5

6

12

7

14

9

int pivotIndex = 0;
if ...
Call Stack #2
Call Stack #1
Call Stack #0

pivot
Index

2

0

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) ...
Call Stack #1
Call Stack #0

pivot
Index

1

2

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < end) {
pivotIndex =...
We are done with these elements!
Call Stack #0

pivot
Index

2

3

3

5

6

12

7

14

9

int pivotIndex = 0;
if (start < ...
pivot
Index
Call Stack #1
Call Stack #0

Walkthrough ends here.
The right hand side is also sorted as it
recursively calls...
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Quicksort: illustrated step-by-step walk through

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A step-by-step illustration of Quicksort to help you walk through a series of operations. Illustration is accompanied by actual code with bold line indicating the current operation.

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Quicksort: illustrated step-by-step walk through

  1. 1. Quicksort algorithm Illustrated walkthrough
  2. 2. Partition function This function does the most of the heavy lifting, so we look at it first, then see it in the context of Quicksort algorithm
  3. 3. [0] [1] [2] [3] [4] [5] 12 7 14 9 10 11 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex;
  4. 4. store Index i begin 12 last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  5. 5. i store Index 0 begin 12 last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  6. 6. i 0 store Index 0 begin 12 last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  7. 7. i store Index 0 0<5 is true 0 begin 12 last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  8. 8. i store Index 0 12 <= 11 is false 0 begin 12 last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  9. 9. i store Index 1 0 begin 12 last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  10. 10. i store Index 1 7 <= 11 is true 0 begin 12 last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  11. 11. i store Index 1 0 begin 12 Swap last 7 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  12. 12. i store Index 1 0 begin 7 Swap last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  13. 13. i 1 store Index 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  14. 14. i store Index 2 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  15. 15. i store Index 2 2<5 is true 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  16. 16. i store Index 2 14 <= 11 is fase 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  17. 17. i store Index 3 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  18. 18. i store Index 3 3<5 is true 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  19. 19. i store Index 3 9 <= 11 is true 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  20. 20. Swap i store Index 3 1 begin 7 last 12 14 9 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  21. 21. Swap i store Index 3 1 begin 7 last 9 14 12 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  22. 22. i store Index 3 2 begin 7 last 9 14 12 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  23. 23. i store Index 4 2 begin 7 last 9 14 12 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  24. 24. 4<5 is true store Index i 4 2 begin 7 last 9 14 12 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  25. 25. 10 <= 11 is true store Index i 4 2 begin 7 last 9 14 12 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  26. 26. Swap i store Index 4 2 begin 7 last 9 14 12 10 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  27. 27. Swap i store Index 4 2 begin 7 last 9 10 12 14 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  28. 28. i store Index 4 3 begin 7 last 9 10 12 14 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  29. 29. i store Index 3 begin 7 5 last 9 10 12 14 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  30. 30. 4<5 is false store Index i 3 begin 7 5 last 9 10 12 14 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  31. 31. Swap i store Index 3 begin 7 5 last 9 10 12 14 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 11
  32. 32. Swap i store Index 3 begin 7 5 last 9 10 11 14 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 12
  33. 33. i store Index 3 begin 7 5 last 9 10 11 14 int storeIndex = begin; for (int i = begin; i < last; i++) { if (array[i] <= array[last]) { Swap(array, i, storeIndex); storeIndex = storeIndex + 1; } } Swap(array, storeIndex, last); return storeIndex; 12
  34. 34. Quicksort algorithm Now we use Partition in the context of Quicksort
  35. 35. pivot Index [0] [1] [2] [3] [4] 9 7 5 11 12 [5] 2 [6] 14 [7] [8] 3 int pivotIndex = 0; if (begin < last) { pivotIndex = Partition(array, begin, last); QuickSort(array, begin, pivotIndex - 1); QuickSort(array, pivotIndex + 1, last); } else { return; } 10 [9] 6
  36. 36. pivot Index 0 9 7 5 11 12 2 14 3 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 6
  37. 37. 0<9 is true pivot Index 0 9 7 5 11 12 2 14 3 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 6
  38. 38. Partition 0..9 pivot Index 0 9 7 5 11 12 2 14 3 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 6
  39. 39. these are <= 6 these are > 6 pivot Index 5 2 3 3 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  40. 40. Call Stack #0 pivot Index 5 2 3 3 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  41. 41. pivot Index Call Stack #1 Call Stack #0 5 2 3 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  42. 42. pivot Index 0 5 2 3 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  43. 43. 0<2 is true pivot Index 0 5 2 3 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  44. 44. Partition 0..2 pivot Index 0 5 2 3 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  45. 45. pivot Index 1 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  46. 46. Call Stack #1 Call Stack #0 pivot Index 1 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  47. 47. Call Stack #2 pivot Index Call Stack #1 Call Stack #0 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  48. 48. Call Stack #2 Call Stack #1 Call Stack #0 pivot Index 0 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  49. 49. Call Stack #2 0<0 is false Call Stack #1 Call Stack #0 pivot Index 0 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  50. 50. Call Stack #2 Call Stack #1 Call Stack #0 pivot Index 0 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  51. 51. Call Stack #1 Call Stack #0 pivot Index 1 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  52. 52. Call Stack #2 pivot Index Call Stack #1 Call Stack #0 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  53. 53. Call Stack #2 Call Stack #1 Call Stack #0 pivot Index 2 0 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  54. 54. 0<0 is false Call Stack #2 Call Stack #1 Call Stack #0 pivot Index 2 0 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  55. 55. Call Stack #2 Call Stack #1 Call Stack #0 pivot Index 2 0 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  56. 56. Call Stack #1 Call Stack #0 pivot Index 1 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } return (at the end of the function. Implicit ‘return’ statement 10 11
  57. 57. We are done with these elements! Call Stack #0 pivot Index 2 3 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11
  58. 58. pivot Index Call Stack #1 Call Stack #0 Walkthrough ends here. The right hand side is also sorted as it recursively calls Quicksort. 2 3 5 6 12 7 14 9 int pivotIndex = 0; if (start < end) { pivotIndex = Partition(array, start, end); QuickSort(array, start, pivotIndex - 1); QuickSort(array, pivotIndex + 1, end); } else { return; } 10 11

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