Opposite or parallel pointers traversing sequences in linear time O(N)
Search pairs or reverse sequences by moving two indices inward or in parallel, pruning suboptimal options in O(1) time without nested loops.
Core Invariant: Maintain the search space invariant: elements outside [left, right] have already been evaluated and eliminated. Advance whichever pointer monotonically improves or resolves the target condition.
Array is unsorted and problem requires contiguous subarrays with sum K (especially with negative numbers; use Prefix Sum + Hash Map instead).
def two_pointers_search(nums: list[int], target: int) -> list[int]:
# Prerequisite: array must be sorted
left, right = 0, len(nums) - 1
while left < right:
curr_sum = nums[left] + nums[right]
if curr_sum == target:
return [left, right]
elif curr_sum < target:
left += 1 # Need larger sum -> move left inward
else:
right -= 1 # Need smaller sum -> move right inward
return []# | Problem | Difficulty | Top Companies↓ | Frequency | Acceptance | |
|---|---|---|---|---|---|---|
| #1 | Two Sum ArrayHash Table | Easy | 100% | 57.8% | ||
| #5 | Longest Palindromic Substring Two PointersStringDynamic ProgrammingManacher | Medium | 100% | 38.2% | ||
| #42 | Trapping Rain Water ArrayTwo PointersDynamic ProgrammingStackMonotonic Stack | Hard | 100% | 67.7% | ||
| #15 | 3Sum ArrayTwo PointersSorting | Medium | 100% | 39.4% | ||
| #11 | Container With Most Water ArrayTwo PointersGreedy | Medium | 100% | 60.4% | ||
| #253 | Meeting Rooms II ArrayTwo PointersGreedySortingHeap (Priority Queue)Prefix Sum | Medium | 100% | 52.7% | ||
| #295 | Find Median from Data Stream Two PointersDesignSortingHeap (Priority Queue)Data Stream | Hard | 100% | 0.6% | ||
| #125 | Valid Palindrome Two PointersString | Easy | 100% | 53.7% | ||
| #283 | Move Zeroes ArrayTwo Pointers | Easy | 100% | 64.1% | ||
| #75 | Sort Colors ArrayTwo PointersSortingQuicksortBubble Sort | Medium | 100% | 70.0% | ||
| #88 | Merge Sorted Array ArrayTwo PointersSorting | Easy | 100% | 55.2% | ||
| #31 | Next Permutation ArrayTwo Pointers | Medium | 100% | 45.6% | ||
| #151 | Reverse Words in a String Two PointersString | Medium | 100% | 57.0% | ||
| #202 | Happy Number Hash TableMathTwo PointersFloyd's Cycle Finding Algorithm | Easy | 100% | 59.9% | ||
| #647 | Palindromic Substrings Two PointersStringDynamic Programming | Medium | 100% | 73.0% | ||
| #141 | Linked List Cycle Hash TableLinked ListTwo PointersFloyd's Cycle Finding Algorithm | Easy | 100% | 54.7% | ||
| #26 | Remove Duplicates from Sorted Array ArrayTwo Pointers | Easy | 100% | 63.2% | ||
| #189 | Rotate Array ArrayMathTwo Pointers | Medium | 100% | 45.2% | ||
| #287 | Find the Duplicate Number ArrayTwo PointersBinary SearchBit ManipulationPigeonhole PrincipleFloyd's Cycle Finding Algorithm | Medium | 90% | 64.6% | ||
| #18 | 4Sum ArrayTwo PointersSorting | Medium | 88% | 41.1% | ||
| #658 | Find K Closest Elements ArrayTwo PointersBinary SearchSliding WindowSortingHeap (Priority Queue) | Medium | 88% | 0.5% | ||
| #696 | Count Binary Substrings Two PointersString | Easy | 100% | 70.5% | ||
| #167 | Two Sum II - Input Array Is Sorted ArrayTwo PointersBinary Search | Medium | 97% | 65.4% | ||
| #567 | Permutation in String Hash TableTwo PointersStringSliding Window | Medium | 95% | 49.2% | ||
| #143 | Reorder List Linked ListTwo PointersStackRecursion | Medium | 89% | 65.7% | ||
| #28 | Find the Index of the First Occurrence in a String Two PointersStringString MatchingZ AlgorithmKnuth–Morris–Pratt AlgorithmBoyer–Moore String-Search Algorithm | Easy | 100% | 46.9% | ||
| #234 | Palindrome Linked List Linked ListTwo PointersStackRecursion | Easy | 93% | 58.3% | ||
| #1048 | Longest String Chain ArrayHash TableTwo PointersStringDynamic ProgrammingSorting | Medium | 100% | 63.3% | ||
| #407 | Trapping Rain Water II ArrayBreadth-First SearchHeap (Priority Queue)Matrix | Hard | 100% | 64.1% | ||
| #977 | Squares of a Sorted Array ArrayTwo PointersSorting | Easy | 92% | 73.9% | ||
| #392 | Is Subsequence Two PointersStringDynamic Programming | Easy | 88% | 0.5% | ||
| #680 | Valid Palindrome II Two PointersStringGreedy | Easy | 100% | 44.5% | ||
| #344 | Reverse String Two PointersString | Easy | 82% | 81.0% | ||
| #881 | Boats to Save People ArrayTwo PointersGreedySortingTimsort | Medium | 87% | 0.6% | ||
| #844 | Backspace String Compare Two PointersStringStackSimulation | Easy | 87% | 50.0% | ||
| #142 | Linked List Cycle II Hash TableLinked ListTwo PointersFloyd's Cycle Finding Algorithm | Medium | 79% | 58.5% | ||
| #345 | Reverse Vowels of a String Two PointersString | Easy | 72% | 61.7% | ||
| #876 | Middle of the Linked List Linked ListTwo Pointers | Easy | 88% | 82.1% | ||
| #160 | Intersection of Two Linked Lists Hash TableLinked ListTwo Pointers | Easy | 75% | 64.2% | ||
| #1963 | Minimum Number of Swaps to Make the String Balanced Two PointersStringStackGreedyBracket Sequences | Medium | 69% | 0.8% | ||
| #986 | Interval List Intersections ArrayTwo PointersSweep Line | Medium | 100% | 73.1% | ||
| #277 | Find the Celebrity Two PointersGraph TheoryInteractive | Medium | 100% | 49.0% | ||
| #16 | 3Sum Closest ArrayTwo PointersSorting | Medium | 100% | 0.5% | ||
| #1570 | Dot Product of Two Sparse Vectors ArrayHash TableTwo PointersDesignLinear Algebra | Medium | 80% | 89.9% | ||
| #475 | Heaters ArrayTwo PointersBinary SearchSorting | Medium | 78% | 42.2% | ||
| #556 | Next Greater Element III MathTwo PointersString | Medium | 66% | 0.4% | ||
| #27 | Remove Element ArrayTwo Pointers | Easy | 63% | 0.6% | ||
| #723 | Candy Crush ArrayTwo PointersMatrixSimulation | Medium | 100% | 77.6% | ||
| #165 | Compare Version Numbers Two PointersString | Medium | 100% | 46.7% | ||
| #82 | Remove Duplicates from Sorted List II Linked ListTwo Pointers | Medium | 100% | 52.1% |
Browse company-specific interview problem lists and recency breakdowns:
Master core algorithmic patterns tested in FAANG & Big Tech coding interviews.
Opposite or parallel pointers traversing sequences in linear time O(N) It is categorized under Fundamentals and features 225 curated interview problems across Easy (62), Medium (132), and Hard (31) difficulties.
Companies frequently asking Two Pointers questions include Google, Amazon, Meta, Microsoft, Bloomberg, TikTok.
Start by studying the algorithmic strategy and template code, then practice Easy and Medium problems before attempting Hard problems under timed conditions.