LeetCode 828: Count Unique Characters of All Substrings of a Given String
A clear explanation of Count Unique Characters of All Substrings using contribution counting with previous and next occurrences.
Tag
Combinatorics
12 notes
LeetCode 923: 3Sum With Multiplicity
A clear explanation of counting index triplets with duplicate values using frequency counts and combinatorics.
LeetCode 920: Number of Music Playlists
A clear explanation of counting valid music playlists using dynamic programming over playlist length and unique songs used.
LeetCode 902: Numbers At Most N Given Digit Set
A clear explanation of counting numbers less than or equal to N using digit-by-digit construction and combinatorics.
LeetCode 891: Sum of Subsequence Widths
A clear explanation of summing subsequence widths by sorting and counting each element as a maximum and minimum.
LeetCode 634: Find the Derangement of An Array
A dynamic programming and combinatorics solution for counting permutations with no fixed positions.
LeetCode 458: Poor Pigs
A clear explanation of the combinatorics behind finding the minimum number of pigs needed to identify the poisonous bucket.
LeetCode 357: Count Numbers with Unique Digits
A clear explanation of counting numbers with unique digits using combinatorics.
LeetCode 276: Paint Fence
A dynamic programming solution for counting ways to paint fence posts with no more than two adjacent posts sharing the same color.
LeetCode 62: Unique Paths
A clear guide to counting unique paths in a grid using dynamic programming.
7.5 Probabilistic and Combinatorial Proofs
Using counting, random choice, and finite structure to prove identities and existence statements.
05. Combinatorics
Counting, arrangement, structure, and extremal behavior of finite and discrete systems.