From 8accdad04152b844f9b7b1487ed3c7948151286a Mon Sep 17 00:00:00 2001
From: "Sakamoto, Kazunori" <exkazuu@gmail.com>
Date: Sat, 16 May 2015 00:44:19 +0900
Subject: [PATCH] Add variance in score board.

---
 app/models/group.rb                     | 35 ++++++++++++++++++++-----
 app/views/contests/scores/show.html.erb |  2 ++
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/app/models/group.rb b/app/models/group.rb
index f470e71..06c1560 100644
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -24,10 +24,10 @@ def attendances_for(contest)
 
   def solved_submission_for(problem, type)
     Submission.where(
-      problem_id: problem.id,
-      problem_type: type,
-      solved: true,
-      attendance_id: Attendance.where(user_id: user_ids).select(:id))
+        problem_id: problem.id,
+        problem_type: type,
+        solved: true,
+        attendance_id: Attendance.where(user_id: user_ids).select(:id))
       .order("score DESC")
       .first
   end
@@ -39,13 +39,34 @@ def solved?(problem, type, attendances = attendances_for(problem.contest))
 
   def score_for(contest)
     Submission.where(
-      problem_id: contest.problem_ids,
-      solved: true,
-      attendance_id: Attendance.where(user_id: user_ids).select(:id))
+        problem_id: contest.problem_ids,
+        solved: true,
+        attendance_id: Attendance.where(user_id: user_ids).select(:id))
       .group(:problem_id, :problem_type)
       .maximum(:score)
       .values
       .sum
   end
 
+  def variance_for(contest)
+    group = Submission.where(
+        problem_id: contest.problem_ids,
+        solved: true,
+        attendance_id: Attendance.where(user_id: user_ids).select(:id))
+      .group(:problem_id, :problem_type)
+      .maximum(:score)
+    uid2score = Hash[user_ids.map { |id| [id, 0] }]
+    group.each do |k, v|
+      s = Submission.where(
+          problem_id: k[0],
+          problem_type: k[1],
+          score: v,
+          solved: true,
+          attendance_id: Attendance.where(user_id: user_ids).select(:id)).first
+      uid2score[s.attendance.user_id] += s.score
+    end
+    avg = uid2score.map { |uid, score| score }.sum.to_f / uid2score.size
+    uid2score.map { |uid, score| (score - avg) * (score - avg) }.sum / uid2score.size
+  end
+
 end
diff --git a/app/views/contests/scores/show.html.erb b/app/views/contests/scores/show.html.erb
index 1ddec3c..1ff08ca 100644
--- a/app/views/contests/scores/show.html.erb
+++ b/app/views/contests/scores/show.html.erb
@@ -7,6 +7,7 @@
     <th class='center'>Place</th>
     <th>Team Name</th>
     <th class='center'>Score</th>
+    <th class='center'>Variance</th>
     <% @problems.each do |problem| %>
       <th class='center'>
         <%= tooltip problem.title do %>
@@ -30,6 +31,7 @@
       <td class='center'><%= index + 1 %></td>
       <td><%= group.name %></td>
       <td class='center'><%= group.score_for(@contest) %></td>
+      <td class='center'><%= group.variance_for(@contest).round(2) %></td>
       <% @problems.each do |problem| %>
         <td class='center'>
           <div>