Add dynamic programming approach 1

dynamic_programming/pascal_triangle_ii.rb

@@ -0,0 +1,53 @@
+# Challenge name: Pascal's triangle ii
+#
+# 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]
+
+#
+# Approach 1: Dynamic Programming
+#
+
+# Complexity Analysis
+#
+# Time complexity: O(k^2).
+# Space complexity: O(k) + O(k) ~ O(k).
+
+# @param {Integer} row_index
+# @return {Integer[]}
+def get_row(row_index)
+  result = generate(row_index)
+  result[result.count - 1]
+end
+
+def generate(num_rows)
+  return [[1]] if num_rows < 1
+  result = [[1], [1, 1]]
+
+  (2...num_rows + 1).each do |row|
+    prev = result[row - 1]
+    current = [1]
+    med = prev.count / 2
+
+    (1...prev.count).each do |i|
+      current[i] = prev[i - 1] + prev[i]
+    end
+
+    current.push(1)
+    result.push(current)
+  end
+
+  result
+end