Python Program for Insertion Sort

In this article, we will learn about the implementation of the Insertion sort in Python 3.x. Or earlier.

Algorithm

1. Iterate over the input elements by growing the sorted array at each iteration.
2. Compare the current element with the largest value available in the sorted array.
3. If the current element is greater, then it leaves the element in its place 
   and moves on to the next element else it finds its correct position in the 
   sorted array and moves it to that position in the array.
4. This is achieved by shifting all the elements towards the right, which are 
   larger than the current element, in the sorted array to one position ahead.

Now let’s see the visual representation of the algorithm −

Now let’s see the implementation

Example

 Live Demo

def insertionSort(arr):
   for i in range(1, len(arr)):
      key = arr[i]
      # Move elements of arr[0..i-1], that are greater than key,
      # to one position ahead of their current position
      j = i-1
      while j >=0 and key < arr[j] :
         arr[j+1] = arr[j]
         j -= 1          
       arr[j+1] = key
# main
arr = ['t','u','t','o','r','i','a','l']
insertionSort(arr)
print ("The sorted array is:")
for i in range(len(arr)):
   print (arr[i])

Output

The sorted array is:
a
i
l
o
r
t
t
u

Time Complexity − O(n^*2)

Auxiliary Space − O(1)

All the variables are declared in the global frame as shown in the figure below −

Conclusion

In this article, we learned about the Insertion sort and its implementation in Python 3.x. or earlier.