Data Structures
DNA Complement Matching
Check whether a DNA strand is its own reverse complement using two pointers from both ends with base-pair matching (A-T, C-G), in O(n) time.
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Data Structures
Is Subsequence Check (Two Pointer)
Check whether one string is a subsequence of another using two pointers in O(n) time and O(1) space.
Data Structures
Interview Concept: Same Direction vs Opposite Direction Two Pointers
Understand the two core two pointer patterns — opposite-direction (converging) and same-direction (fast/slow or read/write) — with when to use each in...
Data Structures
Interview Concept: Fast and Slow Pointer Technique Explained
Master the fast and slow pointer technique (Floyd’s algorithm): detect cycles, find the middle, and locate the nth node from the end, all in O(n) time...
Data Structures
Binary Search (Classic Iterative)
Classic iterative binary search on a sorted array in O(log n) time, with Python, Java and C++ code and an overflow-safe midpoint.
Data Structures
Binary Search (Recursive)
Recursive binary search on a sorted array in O(log n) time with O(log n) call-stack space, in Python, Java and C++.
Data Structures
Search Insert Position
Search Insert Position (LeetCode 35): use lower-bound binary search to find where a target is or should be inserted, in O(log n).
Data Structures
First and Last Position of Element in Sorted Array
Find First and Last Position of a target in a sorted array (LeetCode 34) using two binary searches (lower and upper bound) in O(log n).
Data Structures
Search in Rotated Sorted Array
Search in Rotated Sorted Array (LeetCode 33): modified binary search that identifies the sorted half each step, in O(log n).
Data Structures
Search in Rotated Sorted Array II (With Duplicates)
Search in Rotated Sorted Array II (LeetCode 81) with duplicates: binary search that shrinks ambiguous ends, O(log n) average and O(n) worst case.
Data Structures
Find Minimum in Rotated Sorted Array
Find Minimum in Rotated Sorted Array (LeetCode 153): binary search comparing mid with the right end, in O(log n).
Data Structures
Find Peak Element
Find Peak Element (LeetCode 162): binary search on the slope to find any element greater than its neighbours in O(log n).