Ch 2 · Permutations and Combinations

📘 Core concepts

1. 1Permutation: arrangement (order matters).
2. 2Combination: selection (order does not matter).
3. 3Factorial: n! = n(n−1)(n−2)...1; 0! = 1.
4. 4Circular permutation of n distinct objects = (n−1)!
5. 5Restrictions handled by treating grouped items as one unit or fixing positions.