Shubha 👽

lib/exercises.rb

@@ -1,20 +1,46 @@
-
+require "pry"
 
 # This method will return an array of arrays.
 # Each subarray will have strings which are anagrams of each other
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n * m log m) where m is the number of strings, and m is the length of a string
+# Space Complexity: O(n * m) where n is the number of strings, and m is the length of a string (m space complexity from sort)
 
 def grouped_anagrams(strings)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  buckets = {}
+  strings.each do |str| 
+    sorted = str.chars.sort.join 
+    if buckets[sorted]
+      buckets[sorted] << str
+    else
+      buckets[sorted] = [str]
+    end
+  end
+  return buckets.values
 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: O(n * k), where n is the length of the list and k is the number of common elements to return
+# Space Complexity: O(n + k) where n is the length of the list and k is the number of common elements to return
 def top_k_frequent_elements(list, k)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+  counts = Hash.new(0)
+  top_values = Array.new()
+  list.each do |el| # O(n)
+      counts[el] += 1  
+      index = k - 1
+      index -= 1 until top_values[index + 1] == el if top_values.include?(el) #O(k)      
+      while index >= 0 #O(k)
+        if counts[el] > counts[top_values[index]]
+          temp = top_values[index] 
+          top_values[index] = el
+          top_values[index + 1] = temp if index + 1 < k
+          index -= 1 
+        else
+          break
+        end      
+      end
+  end
+  return top_values
 end
 
 
@@ -23,8 +49,66 @@ 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(n^2) where n is the number of elements in a row, column, or box
+# Space Complexity: O(n) since only one counts hash is used at a time
 def valid_sudoku(table)
-  raise NotImplementedError, "Method hasn't been implemented yet!"
+
+  # check if rows valid
+  table.each do |row|
+    counts = Hash.new(0)
+    row.each do |char|
+      if char.to_i.to_s == char
+        counts[char] += 1
+        return false if counts[char] > 1
+      end
+    end
+  end
+
+  # check if columns valid
+  column = 0
+  while column < 9
+    counts = Hash.new(0)
+    table.each do |row|
+      char = row[column]
+      if char.to_i.to_s == char
+        counts[char] += 1
+        return false if counts[char] > 1
+      end
+    end
+    column += 1
+  end
+
+  # check if boxes valid
+
+  row_start = 0
+  row_end = 3
+
+  while row_end <= 9
+    col_start = 0
+    col_end = 3
+    while col_end <= 9
+
+      # iterate through each value in box to check for duplicates 
+      counts = Hash.new(0)
+      (row_start...row_end).each do |row_index|
+        (col_start...col_end).each do |col_index|
+          char = table[row_index][col_index]
+          if char.to_i.to_s == char
+            counts[char] += 1
+            return false if counts[char] > 1
+          end
+        end
+      end
+
+      # move on to next box in row
+      col_start += 3
+      col_end += 3
+    end
+    # move on to next row of boxes
+    row_start += 3
+    row_end += 3
+  end
+
+
+  return true
 end

test/exercises_test.rb

@@ -68,8 +68,9 @@
     end
   end
 
-  xdescribe "top_k_frequent_elements" do
+  describe "top_k_frequent_elements" do
     it "works with example 1" do
+
       # Arrange
       list = [1,1,1,2,2,3]
       k = 2
@@ -82,6 +83,7 @@
     end
 
     it "works with example 2" do
+
       # Arrange
       list = [1]
       k = 1
@@ -94,6 +96,7 @@
     end
 
     it "will return [] for an empty array" do
+
       # Arrange
       list = []
       k = 1
@@ -106,6 +109,7 @@
     end
 
     it "will work for an array with k elements all unique" do
+
       # Arrange
       list = [1, 2, 3]
       k = 3
@@ -118,6 +122,7 @@
     end
 
     it "will work for an array when k is 1 and several elements appear 1 time (HINT Pick the 1st one)" do
+
       # Arrange
       list = [1, 2, 3]
       k = 1
@@ -131,7 +136,7 @@
 
   end
 
-  xdescribe "valid sudoku" do
+  describe "valid sudoku" do
     it "works for the table given in the README" do
       # Arrange
       table = [