Add controller for Problems with index and show actions

app/controllers/problems_controller.rb

@@ -0,0 +1,21 @@
+class ProblemsController < ApplicationController
+  before_action :set_problem, only: [:show]
+
+  def index
+    @problems = Problem.paginate(page: params[:page])
+  end
+
+  def show
+  end
+
+  private
+  # Use callbacks to share common setup or constraints between actions.
+  def set_problem
+    @problem = Problem.find(params[:id])
+  end
+
+  # Never trust parameters from the scary internet, only allow the white list through.
+  def problem_params
+    params.require(:problem)
+  end
+end