From c2188d46baf8f22c2f1146912d93bd69bb569767 Mon Sep 17 00:00:00 2001
From: Li Dai <li.lea.dai@gmail.com>
Date: Thu, 22 Apr 2021 02:29:46 -0700
Subject: [PATCH] 3 exercises tests passing

---
 lib/exercises.rb       | 88 +++++++++++++++++++++++++++++++++++++-----
 test/exercises_test.rb |  2 +-
 2 files changed, 80 insertions(+), 10 deletions(-)

diff --git a/lib/exercises.rb b/lib/exercises.rb
index e1b3850..ae6d1b7 100644
--- a/lib/exercises.rb
+++ b/lib/exercises.rb
@@ -1,19 +1,49 @@
 
 # This method will return an array of arrays.
 # Each subarray will have strings which are anagrams of each other
-# Time Complexity: ?
-# Space Complexity: ?
+# n => number of strings, m => largest number of characters of a string
+# Time Complexity: n * mlog(m) (sorting n strings: n * mlog(m); lookup, push, assign: O(1), iterating o(n))
+# Space Complexity: n * m (worst case has to create a new array/key for each string, and takes m space to sort it)
 
 def grouped_anagrams(strings)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  anagram_hash = Hash.new 
+  grouped_anagrams = Array.new
+
+  #build a hash table where key is the sorted string and value is an array of the anagrams
+  strings.each_with_index do |string, index|
+    sorted_str = string.chars.sort.join
+    if anagram_hash.key?(sorted_str)
+      anagram_hash[sorted_str] << strings[index]
+    else
+      anagram_hash[sorted_str] = [strings[index]]
+    end
+  end
+
+  anagram_hash.values.each do |anagrams|
+    grouped_anagrams << anagrams
+  end
+
+  return grouped_anagrams
 end
 
 # This method will return the k most common elements
 # in the case of a tie it will select the first occuring element.
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: Olog(n) for sorting
+# Space Complexity: o(n)
 def top_k_frequent_elements(list, k)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  elements_counter = Hash.new(0)
+
+  list.each do |num|
+    elements_counter[num] += 1
+  end
+
+  result_elements = []
+  elements_counter.values.sort.reverse.take(k).each do |frequency|
+    result_elements << elements_counter.key(frequency)
+    elements_counter.delete(elements_counter.key(frequency))
+  end
+
+  return result_elements
 end
 
 
@@ -22,8 +52,48 @@ def top_k_frequent_elements(list, k)
 #   Each element can either be a ".", or a digit 1-9
 #   The same digit cannot appear twice or more in the same 
 #   row, column or 3x3 subgrid
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(1) fixed grid
+# Space Complexity: O(1)
 def valid_sudoku(table)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+
+  #check rows
+  9.times do |r|
+    line_hash = Hash.new(0)
+    9.times do |c|
+      if table[r][c] != "."
+        line_hash[table[r][c]] += 1
+        return false if line_hash[table[r][c]] > 1
+      end
+    end
+  end
+
+  #check columns
+  9.times do |c|
+    column_hash = Hash.new(0)
+    9.times do |r|
+      if table[r][c] != "."
+        column_hash[table[r][c]] += 1
+        return false if column_hash[table[r][c]] > 1
+      end
+    end
+  end
+
+  #check sub-box
+  3.times do |box_r|  
+    3.times do |box_c|
+      box_hash = Hash.new(0)
+      3.times do |r|
+        3.times do |c|
+          row = r + box_r * 3
+          col = c + box_c * 3
+          if table[row][col] != "."
+            box_hash[table[row][col]] += 1
+            return false if box_hash[table[row][col]] > 1
+          end
+        end
+      end
+    end
+  end
+
+  return true
 end
diff --git a/test/exercises_test.rb b/test/exercises_test.rb
index 74646dc..8025075 100644
--- a/test/exercises_test.rb
+++ b/test/exercises_test.rb
@@ -151,7 +151,7 @@
     end
   end
 
-  xdescribe "valid sudoku" do
+  describe "valid sudoku" do
     it "works for the table given in the README" do
       # Arrange
       table = [