problem set + solution

lib/leetcode.rb

@@ -3,6 +3,7 @@
 require 'leetcode/sudoku_solver'
 require 'leetcode/longest_valid_parens'
 require 'leetcode/merge_k_sorted_lists'
+require 'leetcode/first_missing_positive'
 require 'leetcode/reverse_nodes_in_k_group'
 require 'leetcode/median_of_two_sorted_arrays'
 require 'leetcode/regular_expression_matching'

lib/leetcode/first_missing_positive.rb

@@ -0,0 +1,14 @@
+module Leetcode
+  # https://leetcode.com/problems/first-missing-positive/
+  class FirstMissingPositive
+    def execute(nums)
+      lowest = 1
+
+      nums.each do |num|
+        lowest += 1 if num == lowest
+      end
+
+      lowest
+    end
+  end
+end

spec/leetcode/first_missing_positive_spec.rb

@@ -0,0 +1,30 @@
+RSpec.describe Leetcode::FirstMissingPositive do
+  describe '#execute' do
+    let(:nums) { [] }
+    subject { Leetcode::FirstMissingPositive.new.execute(nums)}
+
+    context '[1,2,0]' do
+      let(:nums) { [1,2,0] }
+
+      it do
+        expect(subject).to be 3
+      end
+    end
+
+    context '[3,4,-1,1]' do
+      let(:nums) { [3,4,-1,1] }
+
+      it do
+        expect(subject).to be 2
+      end
+    end
+
+    context '[7,8,9,11,12]' do
+      let(:nums) { [7,8,9,11,12] }
+
+      it do
+        expect(subject).to be 1
+      end
+    end
+  end
+end