Insertion sort is a simple sorting algorithm that builds the final sorted array (or list) one item at a time. It is a comparison-based algorithm that builds a final sorted array one element at a time. It iterates through an input array and removes one element per iteration, finds the place the element belongs in the array, and then places it there.It is generally considered much less efficient on large lists than more advanced algorithms such as quicksort, heapsort, or merge sort although it does has its own advantages - see additional information below.
#1 Write a Python program to sort a list of elements using the Insertion sort algorithm
#2 Comment each line of the python solution below to show your understanding of the algorithm
def insertionSort(nlist): for index in range(1,len(nlist)): currentvalue = nlist[index] position = index while position>0 and nlist[position-1]>currentvalue: nlist[position]=nlist[position-1] position = position-1 nlist[position]=currentvalue nlist = [14,46,43,27,57,41,45,21,70] insertionSort(nlist) print(nlist)
Insertion sort provides several advantages:
When people manually sort cards in a bridge hand, most use a method that is similar to insertion sort
Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list. At each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list, and inserts it there. It repeats until no input elements remain.
Sorting is typically done in-place, by iterating up the array, growing the sorted list behind it. At each array-position, it checks the value there against the largest value in the sorted list (which happens to be next to it, in the previous array-position checked). If larger, it leaves the element in place and moves to the next. If smaller, it finds the correct position within the sorted list, shifts all the larger values up to make a space, and inserts into that correct position.
The resulting array after k iterations has the property where the first k + 1 entries are sorted ("+1" because the first entry is skipped). In each iteration the first remaining entry of the input is removed, and inserted into the result at the correct position, thus extending the result:
with each element greater than x copied to the right as it is compared against x.
The most common variant of insertion sort, which operates on arrays, can be described as follows:
i ← 1 while i < length(A) j ← i while j > 0 and A[j-1] > A[j] swap A[j] and A[j-1] j ← j - 1 end while i ← i + 1 end while