Add brute force approach

data_structures/arrays/good_pairs.rb

@@ -8,16 +8,35 @@
 # @return {Integer}
 #
 
+#
+# Approach 1: Brute Force
+#
+# Time Complexity: O(n^2)
+#
 def num_identical_pairs(nums)
+  count = 0
+  nums.each_with_index do |num, i|
+    target = num
+    nums.each_with_index do |num, j|
+      next if i >= j
+      if num == target
+        count += 1
       end
+    end
+  end
+  count
+end
+
 nums = [1, 2, 3, 1, 1, 3]
 puts(num_identical_pairs(nums))
 # Output: 4
 # Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.
+
 nums = [1, 1, 1, 1]
 puts(num_identical_pairs(nums))
 # Output: 6
 # Explanation: Each pair in the array are good.
+
 nums = [1, 2, 3]
 puts(num_identical_pairs(nums))
 # Output: 0