Combination Function

Introduction

The combination function, nCr, is a count of the number of ways to choose r items out of n distinct items.

For example, 5C3 would represent the number of ways to choose 3 students out of 5 students. If we label the students A, B, C, D, and E. There are 10 possible combinations: (ABC, ABD, ABE, ACD, ACE, ADE, BCE, BCE, BDE, CDE).

Note that ABC and ACB is counted as 1 combination because the order doesn't matter. Hence, 5C3 = 10.