Two Pointer DSA Patterns

My working repo for mastering the Two Pointer technique — part of a 90-day DSA patterns study plan. Each problem lives in its own folder with its code and a dedicated README explaining the approach.

Structure

two-pointer-dsa/ ├── README.md ├── Progress.md ├── notes/ │ └── two_pointer_mastery.md └── solutions/ ├── 01_palindrome_check/ ├── 02_two_sum_sorted/ ├── 03_longest_palindromic_substring/ ├── 04_remove_duplicates/ ├── 05_merge_sorted_arrays/ ├── 06_linked_list_cycle/ └── 07_middle_of_linked_list/ Each solution folder contains a .py file and its own README.md.

The Three Core Templates

1. Opposite ends (toward each other)

left, right = 0, len(arr) - 1
while left < right:
    ...
    left += 1
    right -= 1

2. Two inputs, exhaust both

i, j = 0, 0
while i < len(a) and j < len(b):
    ...
result.extend(a[i:]); result.extend(b[j:])

3. Fast / slow (same direction)

slow = 0
for fast in range(len(arr)):
    if CONDITION:
        slow += 1
        arr[slow] = arr[fast]

Problems Solved

#	Problem	Pattern	Folder
1	Valid Palindrome	Opposite ends	01_palindrome_check/
2	Two Sum II (sorted array)	Opposite ends	02_two_sum_sorted/
3	Longest Palindromic Substring	Expand around center	03_longest_palindromic_substring/
4	Remove Duplicates from Sorted Array	Fast/slow	04_remove_duplicates/
5	Merge Sorted Array	Exhaust both	05_merge_sorted_arrays/
6	Linked List Cycle	Fast/slow	06_linked_list_cycle/
7	Middle of Linked List	Fast/slow	07_middle_of_linked_list/

Practice Backlog

• 3Sum (LeetCode 15)
• Container With Most Water (LeetCode 11)
• Trapping Rain Water (LeetCode 42)
• Move Zeroes (LeetCode 283)

Running

python solutions/01_palindrome_check/palindrome_check.py

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