Question

I use the following algorithm for insertion sort:

def insertionSort(A):
    indices = [z for z in xrange(len(A))]
    for j in range(1, len(A)):
        key = A[j]
        i = j-1
        while (i>=0) and (A[i]<key):
            A[i+1] = A[i]  
            indices[j-i-1] = i+1         
            i = i-1

        A[i+1] = key

However, I need to maintain a list to map the indices of the original values of A to the sorted values of A, which means if I have a list of [1,3,4,2] after sorting the list = [4,3,2,1] i will have a indices list of [3,1,0,2].

Any pointers? I’m kinda stuck.

EDITED: apologies, sorting in descending order..

Answer 1

Why are you writing a sort? Use Python’s builtin sorting.

def sort_with_indexes(data):
    sorted_data = sorted(enumerate(data), key=lambda key: key[1])
    indexes = range(len(data))
    indexes.sort(key=lambda key: sorted_data[key][0])
    return [i[1] for i in sorted_data], indexes

data, indexes = sort_with_indexes([1,3,4,2])
print data, indexes