Counting
40 problems
Counting problems enumerate valid configurations without explicitly generating them. Techniques: combinatorics (nCr), inclusion-exclusion, digit DP, and contribution of each element. In C#, use long to avoid overflow when multiplying counts.
- 299.Bulls and CowsUnknown
- 594.Longest Harmonious SubsequenceEasy
- 726.Number of AtomsHard
- 869.Reordered Power of 2Medium
- 884.Uncommon Words from Two SentencesEasy
- 1079.Letter Tile PossibilitiesMedium
- 1128.Number of Equivalent Domino PairsEasy
- 1267.Count Servers that CommunicateMedium
- 1399.Count Largest GroupUnknown
- 1400.Construct K Palindrome StringsUnknown
- 1636.Sort Array by Increasing FrequencyUnknown
- 1790.Check if One String Swap Can Make Strings EqualEasy
- 1857.Largest Color Value in a Directed GraphHard
- 1922.Count Good NumbersUnknown
- 2131.Longest Palindrome by Concatenating Two Letter WordsMedium
- 2176.Count Equal and Divisible Pairs in an ArrayUnknown
- 2182.Construct String With Repeat LimitMedium
- 2206.Divide Array Into Equal PairsEasy
- 2210.Count Hills and Valleys in an ArrayUnknown
- 2225.Find Players With Zero or One LossesMedium
- 2275.Largest Combination With Bitwise AND Greater Than ZeroMedium
- 2416.Sum of Prefix Scores of StringsHard
- 2529.Maximum Count of Positive Integer and Negative IntegerEasy
- 2799.Count Complete Subarrays in an ArrayMedium
- 2930.Number of Strings Which Can Be Rearranged to Contain SubstringMedium
- 3005.Count Elements With Maximum FrequencyEasy
- 3016.Minimum Number of Pushes to Type Word IIMedium
- 3223.Minimum Length of String After OperationsUnknown
- 3272.Find the Count of Good IntegersUnknown
- 3330.Find the Original Typed String IEasy
- 3335.Total Characters in String After Transformations IMedium
- 3337.Total Characters in String After Transformations IIUnknown
- 3343.Count Number of Balanced PermutationsUnknown
- 3405.Count the Number of Arrays with K Matching Adjacent ElementsUnknown
- 3442.Maximum Difference Between Even and Odd Frequency IMedium
- 3541.Find Most Frequent Vowel and ConsonantUnknown
- 3577.Count the Number of Computer Unlocking PermutationsUnknown
- 3583.Count Special TripletsUnknown
- 3623.Count Number of Trapezoids IUnknown
- 3625.Count Number of Trapezoids IIUnknown