38 lines
995 B
Ruby
38 lines
995 B
Ruby
|
# frozen_string_literal: true
|
||
|
|
|
||
|
|
# Given a non-empty array of int, every element appears twice except for 1. Find that element.
|
||
|
|
# Time: O(n)
|
||
|
|
# Space: O(n)
|
||
|
|
module Arrays
|
||
|
|
def self.single_number(arr)
|
||
|
|
frequency = Hash.new(0)
|
||
|
|
|
||
|
|
arr.each do |num|
|
||
|
|
frequency[num] += 1
|
||
|
|
end
|
||
|
|
|
||
|
|
frequency.each do |num, count|
|
||
|
|
return num if count == 1
|
||
|
|
end
|
||
|
|
|
||
|
|
nil
|
||
|
|
end
|
||
|
|
end
|
||
|
|
|
||
|
|
RSpec.describe Arrays do
|
||
|
|
describe '.single_number' do
|
||
|
|
it 'returns the single number in the array' do
|
||
|
|
expect(Arrays.single_number([1])).to eq(1)
|
||
|
|
expect(Arrays.single_number([1, 2, 2])).to eq(1)
|
||
|
|
expect(Arrays.single_number([1, 2, 1])).to eq(2)
|
||
|
|
expect(Arrays.single_number([4, 2, 2, 3, 4, 1, 1])).to eq(3)
|
||
|
|
expect(Arrays.single_number([5, 5, 6, 6, 7, 7, 8])).to eq(8)
|
||
|
|
end
|
||
|
|
|
||
|
|
it 'returns nil when no single number is found' do
|
||
|
|
expect(Arrays.single_number([1, 1, 2, 2, 3, 3])).to be_nil
|
||
|
|
expect(Arrays.single_number([1, 1, 2, 2, 3, 3, 4, 4])).to be_nil
|
||
|
|
end
|
||
|
|
end
|
||
|
|
end
|