Two-pointer Technique

It is one of the main techniques used for in-place Array algorithms. We can use it to iterate over the Array in two different places at the same time.

And it is also used in the

• Slow and Fast pointer technique

• Sliding Window technique

Example

Reverse an Array

def reverse_array(arr):
    left = 0
    right = len(arr) - 1
    while left < right:
        arr[left], arr[right] = arr[right], arr[left]
        left += 1
        right -= 1

Remove Duplicates from Sorted Array

def remove_duplicates(arr):
    if len(arr) == 0:
        return 0
    left = 0
    for right in range(1, len(arr)):
        if arr[left] != arr[right]:
            left += 1
            arr[left] = arr[right]
    return left + 1

Practice

• Reverse String
• Reverse Vowels of a String
• Remove Duplicates from Sorted Array