Answer:
The algorithm is as follows:
0. Start
1. MyArray = []
2. Input n
3. if n <1 or n > 20:
3.1print("Invalid Size")
4. else:
4.1 for [tex]i = 0[/tex] to n - 1:
 4.1.1 Input MyArray[i]
 4.2 even = []; odd = []
4.3 enum = 0; onum = 0
4.4 for i = 0 to n - 1:
 4.4.1 if i%2 == 0:
 4.4.1.1 even[enum]=list[i]
 4.4.1.2 enum = enum + 1
 4.4.2 else:
 4.4.2.1 odd[onum]=list[i]
 4.4.2.2 onum= onum + 1 Â
4.5 MyArray.clear()
4.6 enum=0
4.7 while even:
 4.7.1 minm = even[0]
 4.7.2 for x in even: Â
 4.7.2.1 if x < minm:
  4.7.2.1.1 minm = x
 4.7.3 MMyArray[enum] = minm
 4.7.4 even.remove(minm)
 4.7.5 enum = enum + 1 Â
4.8 while odd:
 4.8.1 maxm = odd[0]
 4.8.2 for x in odd: Â
 4.8.2.1 if x > maxm:
  4.8.2.1.1 maxm = x
 4.8.3 MMyArray[enum] = maxm
 4.8.4 odd.remove(maxm)
 4.8.5 enum = enum + 1
4.9 for i = 0 to n - 1:
 4.9.1 print MyArray[i]
5. Stop
Explanation:
This starts the algorithm
0. Start
This creates an empty array
1. MyArray = []
This gets input for n (the length of the array)
2. Input n
If n is is less than 1 or greater than 20, then the input is invalid
3. if n <1 or n > 20:
3.1print("Invalid Size")
For valid values of n, we have:
4. else:
The italicized gets input into the array
4.1 for [tex]i = 0[/tex] to n - 1:
 4.1.1 Input MyArray[i]
This creates empty arrays for even index and for odd index
 4.2 even = []; odd = []
This initializes even index and odd index to 0
4.3 enum = 0; onum = 0
This iterates through the array indices
4.4 for i = 0 to n - 1:
If index is even, add array element to even
 4.4.1 if i%2 == 0:
 4.4.1.1 even[enum]=list[i]
 4.4.1.2 enum = enum + 1
If otherwise, add array element to odd
 4.4.2 else:
 4.4.2.1 odd[onum]=list[i]
 4.4.2.2 onum= onum + 1 Â
Clear elements of MyArray
4.5 MyArray.clear()
Set index to 0
4.6 enum=0
Iterate through the even array
4.7 while even:
Set minimum to the first index
 4.7.1 minm = even[0]
Sort the array in ascending order
 4.7.2 for x in even: Â
 4.7.2.1 if x < minm:
  4.7.2.1.1 minm = x
Add the sorted array into MyArray
 4.7.3 MMyArray[enum] = minm
Delete the elements of even array
 4.7.4 even.remove(minm)
 4.7.5 enum = enum + 1 Â
Iterate through the odd array
4.8 while odd:
Set maximum to the first index
 4.8.1 maxm = odd[0]
Sort the array in descending order
 4.8.2 for x in odd: Â
 4.8.2.1 if x > maxm:
  4.8.2.1.1 maxm = x
Add the sorted array into MyArray
 4.8.3 MMyArray[enum] = maxm
Delete the elements of odd array
 4.8.4 odd.remove(maxm)
 4.8.5 enum = enum + 1
Iterate through the indices of the double sorted MyArray
4.9 for i = 0 to n - 1:
Print each array element
 4.9.1 print MyArray[i]
End algorithm
5. Stop
See attachment for the program implemented in Python
