Sliding Window & Two Pointers

A sliding window keeps a range of an array or string and moves its two ends forward instead of re-checking every subarray. Two pointers is the same habit applied to one or two sequences at once. Both turn many brute-force scans into a single pass.

The six chapters start with fixed-length windows, move on to windows that grow and shrink, then cover two pointers on one sequence, two pointers on two sequences, three pointers, and grouped iteration. It is the first plan on the route, so it suits anyone starting LeetCode or coming back after a break.

194 problemsRating 1165–28066 Chapters

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I. Fixed-Length Sliding Window

§1.1 Fundamentals

Problem	Rating
1456. Maximum Number of Vowels in a Substring of Given Length	1263
643. Maximum Average Subarray I	1263
1343. Number of Sub Arrays of Size K AND Average Greater Than OR Equal to Threshold	1317
2090. K Radius Subarray Averages	1358
2379. Minimum Recolors to Get K Consecutive Black Blocks	1360
2841. Maximum Sum of Almost Unique Subarray	1546
2461. Maximum Sum of Distinct Subarrays with Length K	1553
1423. Maximum Points You Can Obtain From Cards	1574

§1.2 Advanced (Optional)Optional

Problem	Rating
3679. Minimum Discards to Balance Inventory	1639
1052. Grumpy Bookstore Owner	1639
3439. Reschedule Meetings for Maximum Free Time I	1729
3694. Distinct Points Reachable After Substring Removal	1739
3652. Best Time to Buy AND Sell Stock Using Strategy	1739
2134. Minimum Swaps to Group All 1s Together II	1748
1652. Defuse the Bomb	1748
1297. Maximum Number of Occurrences of a Substring	1748
2653. Sliding Subarray Beauty	1786
1888. Minimum Number of Flips to Make the Binary String Alternating	2006
567. Permutation in String	2006
438. Find All Anagrams in a String	2006
30. Substring with Concatenation of All Words	2006
2156. Find Substring with Given Hash Value	2063
2953. Count Complete Substrings	2449
1016. Binary String with Substrings Representing 1 to N	2063

§1.3 Miscellaneous (Optional)Optional

Problem	Rating
2200. Find All K Distant Indices in an Array	1266
2269. Find the K Beauty of a Number	1280
1984. Minimum Difference Between Highest AND Lowest of K Scores	1306
1461. Check If a String Contains All Binary Codes of Size K	1504
220. Contains Duplicate III	1504

II. Dynamic-Length Sliding Window

§2.1 Shorter is Valid / Maximize Length

Problem	Rating
3. Longest Substring Without Repeating Characters	1263
3090. Maximum Length Substring with Two Occurrences	1329
1493. Longest Subarray of 1s After Deleting One Element	1423
3634. Minimum Removals to Balance Array	1453
1208. Get Equal Substrings Within Budget	1497
904. Fruit Into Baskets	1516
1695. Maximum Erasure Value	1529
2958. Length of Longest Subarray with at Most K Frequency	1535
2024. Maximize the Confusion of an Exam	1643
1004. Max Consecutive Ones III	1656
1658. Minimum Operations to Reduce X to Zero	1817
2730. Find the Longest Semi Repetitive Substring	1638
2779. Maximum Beauty of an Array After Applying Operation	1638
1838. Frequency of the Most Frequent Element	1876
2516. Take K of Each Character From Left AND Right	1948
2831. Find the Longest Equal Subarray	1976
2271. Maximum White Tiles Covered by a Carpet	2022
2106. Maximum Fruits Harvested After at Most K Steps	2062
2555. Maximize Win From Two Segments	2081
2009. Minimum Number of Operations to Make Array Continuous	2084
1610. Maximum Number of Visible Points	2147
2781. Length of the Longest Valid Substring	2204
3411. Maximum Subarray with Equal Products	2300
3413. Maximum Coins From K Consecutive Bags	2374
395. Longest Substring with at Least K Repeating Characters	2444
1763. Longest Nice Substring	2444
2968. Apply Operations to Maximize Frequency Score	2444
1040. Moving Stones Until Consecutive II	2456

§2.2 Longer is Valid / Minimize Length

Problem	Rating
209. Minimum Size Subarray Sum	1263
2904. Shortest AND Lexicographically Smallest Beautiful String	1914
1234. Replace the Substring for Balanced String	1878
2875. Minimum Size Subarray in Infinite Array	1914
76. Minimum Window Substring	1592
632. Smallest Range Covering Elements From K Lists	1592

§2.3 Counting Subarrays

Problem	Rating
713. Subarray Product Less Than K	1263
3258. Count Substrings That Satisfy K Constraint I	1808
2302. Count Subarrays with Score Less Than K	1808
2762. Continuous Subarrays	1940
1358. Number of Substrings Containing All Three Characters	1646
2962. Count Subarrays Where Max Element Appears at Least K Times	1701
3306. Count Substrings with K Frequency Characters I	1701
2799. Count Complete Subarrays in an Array	1892
2537. Count the Number of Good Subarrays	1892
3298. Count Substrings That Can Be Rearranged to Contain a String II	1909
930. Binary Subarrays with Sum	1592
1248. Count Number of Nice Subarrays	1624
3306. Count of Substrings Containing Every Vowel AND K Consonants II	2200
992. Subarrays with K Different Integers	2210

§2.4 Miscellaneous (Optional)Optional

Problem	Rating
825. Friends of Appropriate Ages	1697
2401. Longest Nice Subarray	1750
1156. Swap for Longest Repeated Character Substring	1787
424. Longest Repeating Character Replacement	1787
438. Find All Anagrams in a String	1787
1712. Ways to Split Array Into Three Subarrays	2079

III. Single-Sequence Two Pointers

§3.1 Opposite Direction Two Pointers

Problem	Rating
344. Reverse String	1263
3643. Flip Square Submatrix Vertically	1235
541. Reverse String II	1263
557. Reverse Words in a String III	1263
345. Reverse Vowels of a String	1263
917. Reverse Only Letters	1263
125. Valid Palindrome	1263
1750. Minimum Length of String After Deleting Similar Ends	1502
2105. Watering Plants II	1507
977. Squares of a Sorted Array	1263
658. Find K Closest Elements	1263
1471. The K Strongest Values in an Array	1263
167. Two Sum II Input Array Is Sorted	1263
633. Sum of Square Numbers	1263
2824. Count Pairs Whose Sum Is Less Than Target	1263
2563. Count the Number of Fair Pairs	1263
15. 3sum	1263
16. 3sum Closest	1263
18. 4sum	1263
611. Valid Triangle Number	1263
1577. Number of Ways Where Square of Number Is Equal to Product of Two Numbers	1263
923. 3sum with Multiplicity	1711
948. Bag of Tokens	1762
11. Container with Most Water	1263
42. Trapping Rain Water	1263
1616. Split Two Strings to Make Palindrome	1868
1498. Number of Subsequences That Satisfy the Given Sum Condition	2276
1782. Count Pairs of Nodes	2457

§3.2 Same Direction Two Pointers

Problem	Rating
611. Valid Triangle Number	1263
3649. Number of Perfect Pairs	1716
1574. Shortest Subarray to Be Removed to Make Array Sorted	1932
2972. Count the Number of Incremovable Subarrays II	2153
2122. Recover the Original Array	2159
2234. Maximum Total Beauty of the Gardens	2562

§3.3 Two Pointers Expanding Outward

Problem	Rating
1793. Maximum Score of a Good Subarray	1946
976. Largest Perimeter Triangle	1263

§3.4 In-Place Modification

Problem	Rating
27. Remove Element	1263
26. Remove Duplicates From Sorted Array	1263
80. Remove Duplicates From Sorted Array II	1263
2273. Find Resultant Array After Removing Anagrams	1295
3684. Maximize Sum of at Most K Distinct Elements	1263
283. Move Zeroes	1263
905. Sort Array by Parity	1263
922. Sort Array by Parity II	1263
3467. Transform Array by Parity	1263
2460. Apply Operations to an Array	1263
1089. Duplicate Zeros	1263
75. Sort Colors	1263

IV. Two-Sequence Two Pointers

§4.1 Two Pointers

Problem	Rating
2109. Adding Spaces to a String	1315
2540. Minimum Common Value	1315
88. Merge Sorted Array	1315
2570. Merge Two 2D Arrays by Summing Values	1315
350. Intersection of Two Arrays II	1315
1855. Maximum Distance Between a Pair of Values	1515
1385. Find the Distance Value Between Two Arrays	1315
925. Long Pressed Name	1315
809. Expressive Words	1605
2337. Move Pieces to Obtain a String	1693
777. Swap Adjacent in Lr String	1693
844. Backspace String Compare	1315
986. Interval List Intersections	1315
1537. Get the Maximum Score	1961

§4.2 Subsequence Validation

Problem	Rating
392. Is Subsequence	1315
524. Longest Word in Dictionary Through Deleting	1315
2486. Append Characters to String to Make Subsequence	1363
2825. Make String a Subsequence Using Cyclic Increments	1415
1023. Camelcase Matching	1537
3132. Find the Integer Added to Array II	1620
522. Longest Uncommon Subsequence II	1700
1898. Maximum Number of Removable Characters	1913
2565. Subsequence with the Minimum Score	2432
3302. Find the Lexicographically Smallest Valid Sequence	2474

V. Three Pointers

Fundamentals

Problem	Rating
2367. Number of Arithmetic Triplets	1263
2563. Count the Number of Fair Pairs	1721
795. Number of Subarrays with Bounded Maximum	1817
2444. Count Subarrays with Fixed Bounds	2093
3347. Maximum Frequency of an Element After Performing Operations II	2156

Advanced Explorations

Problem	Rating
3464. Maximize the Distance Between Points on a Square	2806

VI. Grouped Iteration

Fundamentals

Problem	Rating
485. Max Consecutive Ones	1263
1446. Consecutive Characters	1165
1869. Longer Contiguous Segments of Ones Than Zeros	1205
2414. Length of the Longest Alphabetical Continuous Substring	1222
3456. Find Special Substring of Length K	1244
2273. Find Resultant Array After Removing Anagrams	1295
2348. Number of Zero Filled Subarrays	1316
1513. Number of Substrings with Only 1s	1351
1957. Delete Characters to Make Fancy String	1358
674. Longest Continuous Increasing Subsequence	1263
3708. Longest Fibonacci Subarray	1381
696. Count Binary Substrings	1263
978. Longest Turbulent Subarray	1393
2110. Number of Smooth Descent Periods of a Stock	1408
228. Summary Ranges	1263
2760. Longest Even Odd Subarray with Threshold	1420
1887. Reduction Operations to Make the Array Elements Equal	1428
845. Longest Mountain in Array	1437
2038. Remove Colored Pieces If Both Neighbors Are the Same Color	1468
2900. Longest Unequal Adjacent Groups Subsequence I	1469
1759. Count Number of Homogenous Substrings	1491
3011. Find If Array Can Be Sorted	1497
1578. Minimum Time to Make Rope Colorful	1574
1839. Longest Substring of All Vowels in Order	1580
2765. Longest Alternating Subarray	1581
3255. Find the Power of K Size Subarrays II	1595
3350. Adjacent Increasing Subarrays Detection II	1600
3105. Longest Strictly Increasing OR Strictly Decreasing Subarray	1600
838. Push Dominoes	1638
467. Unique Substrings in Wraparound String	1700
3499. Maximize Active Section with Trade I	1729
413. Arithmetic Slices	1263
68. Text Justification	1263
135. Candy	1263
2948. Make Lexicographically Smallest Array by Swapping Elements	2047
2593. Find Score of an Array After Marking All Elements	1263
3640. Trionic Array II	2278

Every new route opens at the first section of this plan, and its three optional sections are marked and saved for the advanced lists, so they never hold you back.

Ratings come from zerotrac's LeetCode contest ratings. Some problems have no zerotrac rating and are marked Unrated.

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