Two Pointers Notes

Two Sum II - Input Array Is Sorted

Learn how to solve Two Sum II (Input Array Is Sorted) using the two pointer technique in O(n) time and O(1) space, with a clear walkthrough and Python...

Data Structures

Valid Palindrome (Two Pointer Check)

Check if a string is a valid palindrome using two pointers, ignoring case and non-alphanumeric characters, in O(n) time and O(1) space.

Data Structures

Reverse Vowels of a String

Reverse only the vowels of a string in place using two pointers, in O(n) time.

Data Structures

Remove Element In Place

Remove all occurrences of a value from an array in place using the slow/fast two pointer pattern, returning the new length in O(n).

Data Structures

Move Zeroes Using Two Pointers

Move all zeroes to the end of an array while keeping the order of non-zero elements, using two pointers in O(n) time and O(1) space.

Data Structures

3Sum Closest

Find the sum of three integers closest to a target using sorting plus the two pointer technique, in O(n^2) time.

Data Structures

4Sum

Find all unique quadruplets that sum to a target using sorting, nested loops, and two pointers, in O(n^3) time.

Data Structures

Sort Array By Parity

Rearrange an array so even numbers come before odd numbers using two pointers, in place in O(n) time.

Data Structures

Squares of a Sorted Array

Return the squares of a sorted array in sorted order using two pointers from both ends, in O(n) time.

Data Structures

Merge Two Sorted Arrays (Two Pointer)

Merge two sorted arrays in place using two pointers from the back, in O(m+n) time and O(1) space.

Data Structures

Intersection of Two Arrays II

Find the intersection of two arrays including duplicates using sorting and two pointers, in O(n log n) time.

Data Structures

Backspace String Compare

Compare two strings containing backspace characters using two pointers scanning from the end, in O(n) time and O(1) space.