Quiz: Quicksort the following array in ascending order:
54 27 87 58 35 91 28 95 58 86 76 32 19

Example:
6   5   9   8   3   1   7
p   l                   r
decrement r until you find a number <=6
increment l until you find a number >6
6   5   9   8   3   1   7
p       l           r    
swap the numbers at l'th and r'th positions
6   5   1   8   3   9   7
p           l   r    
6   5   1   3   8   9   7
p           l   r    

Swap p and l, repeat recursively on the subarrays 
3   5   1   |6|   8   9   7
            l=r  

-> 
3   5   1 			
p   l   r
decrement r until you find a number <=3
increment l until you find a number > 3
swap l and r
3   1   5
p   l   r

3   1   5
p  l=r

Swap p and l
1   |3|   5

->
8   9   7
p   l   r
no increment or decrement needed
Swap l and r
8   7   9
p   l   r

8   7   9
p  l=r

Swap p and l
7   |8|   9

 -> Sorted array:
 1 |3| 5 |6| 7 |8| 9