Arrays

array_problems/arrays.rb

@@ -3,11 +3,35 @@
 
 module ArrayUtil
   def self.max(array)
+    return nil if array.count == 0 
+    max = array[0]
+    array.each_index do |index|
+      if array[index] > max
+        max = array[index]
+      end
+    end
+    max
   end
 
   def self.middle_element(array)
+    return nil if array.count == 0
+    return array[0] if array.count == 1
+    length = array.count
+    if length % 2 == 0
+      first_middle = (length / 2).to_i - 1
+      second_middle = first_middle + 1
+      (array[first_middle] + array[second_middle]) / 2.0
+    else
+      array[length / 2]
+    end
   end
 
   def self.sum_arrays(array1, array2)
+    return array1 if array1.count == 0
+    sum = []
+    array1.each_index do |index|
+      sum.push(array1[index] + array2[index])
+    end
+    sum
   end
 end

set1/set1.rb

@@ -1,10 +1,43 @@
 module Set1
+  # Big O notation: O(n)
   def self.swap_small(array)
+    return array if array.length == 1
+    array.each_index do |index|
+      if array[index] < array[0]
+        temp = array[0]
+        array[0] = array[index]
+        array[index] = temp
+      end
+    end
   end
 
+  # Big O notation: O(n^2)
   def self.find_sum_2(array, sum = 0)
+    return false if array.length == 0
+    return true if (array.length == 1) && (array[0] == 0)
+
+    array.each_index do |index|
+      return true if array[index] == 0
+      array.each_index do |second_index|
+        return true if array[index] + array[second_index] == 0
+      end
+    end
+    false
   end
 
+  # Big O notation: O(n^3)
   def self.find_sum_3(array)
+    return false if array.length == 0
+    return true if (array.length == 1) && (array[0] == 0)
+
+    array.each_index do |index|
+      return true if array[index] == 0
+      array.each_index do |second_index|
+        array.each_index do |third_index|
+          return true if array[index] + array[second_index] + array[third_index] == 0
+        end
+      end
+    end
+    false
   end
 end

set1/spec/set1_spec.rb

@@ -24,48 +24,48 @@
   end
 
   describe ".find_sum_2" do
-    xit "should return false for an empty array" do
+    it "should return false for an empty array" do
       expect(Set1.find_sum_2([])).to eq(false)
     end
 
-    xit "should return true for an array with just the number 0" do
+    it "should return true for an array with just the number 0" do
       expect(Set1.find_sum_2([0])).to eq(true)
     end
 
-    xit "should return true for an array with the number 0 in it" do
+    it "should return true for an array with the number 0 in it" do
       expect(Set1.find_sum_2([5, 2, 0, -100])).to eq(true)
     end
 
-    xit "should return true if a number and it's negative are in the arrray" do
+    it "should return true if a number and it's negative are in the arrray" do
       expect(Set1.find_sum_2([5, 20, -5, 100])).to eq(true)
       expect(Set1.find_sum_2([5, 20, -3, 100, -20, 2])).to eq(true)
     end
 
-    xit "should return false if none of the numbers add to 0" do
+    it "should return false if none of the numbers add to 0" do
       expect(Set1.find_sum_2([5, 6, 7, 8, -1, -2, -3, -4])).to eq(false)
     end
   end
 
   describe ".find_sum_3" do
-    xit "should return false for an empty array" do
+    it "should return false for an empty array" do
       expect(Set1.find_sum_3([])).to eq(false)
     end
 
-    xit "should return true for an array with just the number 0" do
+    it "should return true for an array with just the number 0" do
       expect(Set1.find_sum_3([0])).to eq(true)
     end
 
-    xit "should return true for an array with the number 0 in it" do
+    it "should return true for an array with the number 0 in it" do
       expect(Set1.find_sum_3([5, 2, 0, -100])).to eq(true)
     end
 
-    xit "should return true if 3 numbers in the array add to 0" do
+    it "should return true if 3 numbers in the array add to 0" do
       expect(Set1.find_sum_3([10, 2, 100, -200, -102, 5])).to eq(true)
       expect(Set1.find_sum_3([10, -51, 100, -201, 102, 5])).to eq(true)
       expect(Set1.find_sum_3([10, 51, 100, -201, -102, 5])).to eq(true) # 51, 51, -102
     end
 
-    xit "should return false if no 3 numbers in the array add to 0" do
+    it "should return false if no 3 numbers in the array add to 0" do
       expect(Set1.find_sum_3([10, 51, 100, 201, 102, 5])).to eq(false)
     end
   end