Advanced · Sorting algorithms · 170 of 264
Insertion sort, step by step
Insertion sort: take each number from the second one on and move it left until it is in place. Print the list after each number is inserted.
Input: whole numbers on one line (at least 2). Output: the list after each insertion.
Examples
3 1 2
1 3 2 1 2 3
1 2 3
1 2 3 1 2 3
4 3 2 1
3 4 2 1 2 3 4 1 1 2 3 4
One more test checks other inputs when you press Check.
Stuck? The idea behind sorting algorithms
Bubble sort swaps neighbours that are in the wrong order, pass after pass. Insertion sort takes each item in turn and slides it back into place among those before it. Merge sort splits the list, sorts each half and merges them.
These exercises ask for the steps, not just the result: write the algorithm yourself rather than calling sorted().
a = [5, 1, 4, 2]
for end in range(len(a) - 1, 0, -1):
for i in range(end):
if a[i] > a[i + 1]:
a[i], a[i + 1] = a[i + 1], a[i]
print(a)Watch for: Off-by-one: comparing a[i] with a[i + 1] means i must stop one before the end.