Two Pointers coding problems

Two-pointer problems walk an array from both ends or at two speeds to cut an O(n²) idea down to O(n): pair sums, removing duplicates, merging sorted lists and partitioning.

35 problems: 10 easy, 21 medium, 4 hard. Free to read; a free account solves them and earns XP and Aura.

1. Count Pairs with Smaller SumPractice · +10 XP · two pointers, sorting, countingeasy
2. Count Pairs with Specific SumPractice · +10 XP · sliding window, two pointers, arrayseasy
3. Find Duplicate in Sorted ArrayPractice · +10 XP · two pointers, arrays, binary searcheasy
4. Find First Element Greater Than KPractice · +10 XP · two pointers, binary search, sorted arrayeasy
5. Find First Even NumberPractice · +10 XP · two pointers, arrays, searchingeasy
6. Find Pair with SumPractice · +10 XP · two pointers, array, two sumeasy
7. Find Smallest Missing Positive IntegerPractice · +10 XP · two pointers, binary search, arrayseasy
8. Reverse Array ElementsPractice · +10 XP · two pointers, array manipulation, beginnereasy
9. Sum of Adjacent ElementsPractice · +10 XP · two pointers, arrays, loopseasy
10. Two Pointers SumPractice · +10 XP · two pointers, arrays, two sumeasy
11. Array of SubarraysDaily · +15 XP · +5 Aura (late, half) · hash map, two pointers, subarray2 solvedmedium
12. Count Subarrays with Distinct ElementsPractice · +20 XP · hash map, sliding window, two pointersmedium
13. Count Unique Element PairsPractice · +20 XP · hash map, two pointers, sortingmedium
14. Cycle Detection and RendezvousPractice · +20 XP · linked structures, cycle detection, two pointersmedium
15. Find First Duplicate Entry PointPractice · +20 XP · linked structures, cycle detection, two pointersmedium
16. K-th Node in CyclePractice · +20 XP · linked structures, cycles, two pointersmedium
17. Longest Sorted SubsegmentPractice · +20 XP · two pointers, arrays, sliding windowmedium
18. Longest Subarray with Alternating ParityPractice · +20 XP · sliding window, two pointers, paritymedium
19. Longest Subarray with At Most K Distinct ElementsPractice · +20 XP · two pointers, sliding window, hash mapmedium
20. Longest Subarray with Bounded DifferencePractice · +20 XP · two pointers, sliding window, data structuresmedium
21. Longest Subarray with Constant DifferencePractice · +20 XP · two pointers, greedy, arraysmedium
22. Longest Subarray with Increasing SumPractice · +20 XP · two pointers, subarray, sliding windowmedium
23. Longest Subarray with Limited DifferencePractice · +20 XP · two pointers, sliding window, greedymedium
24. Longest Subarray with Sum at Most KPractice · +20 XP · sliding window, prefix sums, two pointersmedium
25. Longest Symmetric SubstringPractice · +20 XP · strings, dynamic programming, two pointersmedium
26. Max Consecutive SumPractice · +20 XP · two pointers, dynamic programming, greedymedium
27. Minimize Maximum Difference in PairsPractice · +20 XP · greedy, sorting, two pointersmedium
28. Optimal Apartment RentalPractice · +20 XP · binary search, two pointersmedium
29. Optimal Training ScheduleOpen now · Weekly · +40 XP · +15 Aura · two pointers, sliding window, prefix sum1 solvedmedium
30. Pairs with Same ParityPractice · +20 XP · sorting, two pointers, combinatoricsmedium
31. String BalancePractice · +20 XP · strings, two pointersmedium
32. Distinct Subarrays with Bounded SumPractice · +30 XP · two pointers, hash map, combinatoricshard
33. Longest Subarray with Distinct ElementsPractice · +30 XP · hash map, sliding window, two pointershard
34. Longest Subarray with Equal Number of Zeroes and OnesPractice · +30 XP · two pointers, prefix sum, hash maphard
35. Minimum Window SubstringPractice · +30 XP · sliding window, two pointers, stringshard