0077-combinations.rb

# frozen_string_literal: true

# 77. Combinations
# https://leetcode.com/problems/combinations
# Medium

=begin
Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].

You may return the answer in any order.

Example 1:
Input: n = 4, k = 2
Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
Explanation: There are 4 choose 2 = 6 total combinations.
Note that combinations are unordered, i.e., [1,2] and [2,1] are considered to be the same combination.

Example 2:
Input: n = 1, k = 1
Output: [[1]]
Explanation: There is 1 choose 1 = 1 total combination.

Constraints:
* 1 <= n <= 20
* 1 <= k <= n
=end

# @param {Integer} n
# @param {Integer} k
# @return {Integer[][]}
defcombine(n,k)
return(1..n).map{ |i| [i]}ifk == 1

i=n
result=[]

whilei > 1
result += combine(i - 1,k - 1).map{ |tuple| tuple + [i]}
i -= 1
end

result
end

# **************** #
# TEST #
# **************** #

require"test/unit"
classTest_combine < Test::Unit::TestCase
deftest_
assert_equal[[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]].sort,combine(4,2).sort
assert_equal[[1]],combine(1,1)
end
end