Merge pull request #157 from TheAlgorithms/pascal-triangle-ii-math-approach

DIRECTORY.md

@@ -103,6 +103,7 @@
   * [Find Min](https://github.com/TheAlgorithms/Ruby/blob/master/maths/find_min.rb)
   * [Lucas Series](https://github.com/TheAlgorithms/Ruby/blob/master/maths/lucas_series.rb)
   * [Number Of Digits](https://github.com/TheAlgorithms/Ruby/blob/master/maths/number_of_digits.rb)
+  * [Pascal Triangle Ii](https://github.com/TheAlgorithms/Ruby/blob/master/maths/pascal_triangle_ii.rb)
   * [Power Of Two](https://github.com/TheAlgorithms/Ruby/blob/master/maths/power_of_two.rb)
   * [Prime Number](https://github.com/TheAlgorithms/Ruby/blob/master/maths/prime_number.rb)
   * [Roman To Integer](https://github.com/TheAlgorithms/Ruby/blob/master/maths/roman_to_integer.rb)

maths/pascal_triangle_ii.rb

@@ -0,0 +1,45 @@
+# Given an integer row_index, return the rowIndexth (0-indexed) row of the Pascal's triangle. 
+
+# Example 1:
+#
+# Input: row_index = 3
+# Output: [1,3,3,1]
+#
+# Example 2:
+#
+# Input: row_index = 0
+# Output: [1]
+#
+# Example 3:
+#
+# Input: row_index = 1
+# Output: [1,1]
+
+# Complexity Analysis
+# 
+# Time complexity: O(k).
+# Space complexity: O(k).
+
+def get_row(row_index)
+  (0..row_index).map {|num| combination(row_index, num) }
+end
+
+def combination(num1, num2)
+  factorial(num1) / (factorial(num2) * factorial(num1 - num2))
+end
+
+def factorial(num)
+  (1..num).inject(1) { |res, i| res * i }
+end
+
+row_index = 3
+print(get_row(row_index))
+# => [1,3,3,1]
+
+row_index = 0
+print(get_row(row_index))
+# => [1]
+
+row_index = 1
+print(get_row(row_index))
+# => [1,1]