Term

Permutation

Index

All notes

2026.04.28

Matrix 6 min read

Matrix #4: Matrix Problems — Fibonacci Subarray Sums, Gaussian Elimination & Expected Value

Hard matrix problems: Fibonacci squared subarray sum with segment-tree 4-tuple and companion matrix; cycle-decomposition partition state space for random-swap sorting, first-step analysis, and Gaussian elimination.

#math #matrix #segment-tree #gaussian-elimination #expected-value

2026.04.24

Combinatorics 9 min read

Combinatorics #1.1: Permutations and Combinations

Hockey Stick identity, addition/multiplication principles, binomial identities, example problems: bitonic sequences, multiset permutations, multi-layer coloring DP, CCPC Subpermutation.

#math #combinatorics #permutation #combination #hockey-stick