Insertion Sort Python (original) (raw)
Last Updated : 12 Nov, 2025
Insertion Sort is a simple and intuitive sorting algorithm that works by building a sorted list one element at a time. It takes each element from the unsorted portion and inserts it into the correct position in the sorted portion.
Insertion Sort
How Insertion Sort Works
- Start from the second element (as the first one is already considered sorted).
- Compare the current element (called key) with the elements before it.
- Shift all larger elements one position to the right.
- Insert the key into its correct position.
- Repeat until the entire array is sorted.
Python Implementation
Python `
def insertionSort(arr): n = len(arr)
if n <= 1:
return
for i in range(1, n):
key = arr[i]
j = i - 1
while j >= 0 and key < arr[j]:
arr[j + 1] = arr[j]
j -= 1
arr[j + 1] = key arr = [12, 11, 13, 5, -1] insertionSort(arr) print(arr)
`
Output
[-1, 5, 11, 12, 13]
**Explanation:
- **for i in range(1, n): Iterates through the array from the second element onward.
- **key = arr[i]: Stores the current element to be inserted in the sorted portion.
- **Inner while loop: Shifts elements greater than key one position to the right.
- **arr[j + 1] = key: Inserts key into its correct sorted position.