import random

# find the index of the minimum in L
def my_min_index(L):
  curr_min_index = 0
  for i in range(1,len(L)):
    if (L[i] < L[curr_min_index]):
        curr_min_index = i
  return curr_min_index

# swap the contents of L[i] and L[j]
def swap(L, i, j):
  temp = L[i]; L[i] = L[j]; L[j] = temp

# sort a list in O(n^2) time
def selection_sort(L):
  n = len(L)
  for i in range(n):
      j = i + my_min_index(L[i:])
      swap(L, i, j)

# take two sorted lists and create a single sorted list
def merge(A, B):
    result = []
    i = 0; j = 0
    # correctly interleave the input lists by repeatedly identifying 
    # the smaller one and saving it to our result list
    while ((i < len(A)) and (j < len(B))):
        if (A[i] <= B[j]):
            result.append(A[i])
            i = i + 1
        else:
            result.append(B[j])
            j = j + 1
    # adding two lists just concatenates them, even if one is empty
    result += B[j:]
    result += A[i:]
    return result

# sort a list in O(n log n) time
def merge_sort(L):
    n = len(L)
    # base case: if the list has one element, we don't need to do anything
    if (n <= 1):
        return L
    # recursive case: sort two halves, and merge the result
    else:         
        A = merge_sort(L[:n/2]) #L[0..n/2-1]
        B = merge_sort(L[n/2:]) #L[n/2..n-1] 
        return merge(A, B)


'''
mylist = ['a','b','c','d','e','f']
print mylist  # 0..5

print mylist[2:]  #2..5
'''

mylist = range(20)
random.shuffle(mylist)      
print mylist   
# run selection sort
# Works "in place", it sorts the input list
selection_sort(mylist) 
print "mylist after selection_sort: ", mylist  
    
    
mylist = range(20)  
sortedList = merge_sort(mylist)
print "sortedList after merge_sort: ", sortedList