add brute force approach

dynamic_programming/pascal_triangle_ii.rb

@@ -15,7 +15,37 @@
 # Output: [1,1]
 
 #
-# Approach 1: Dynamic Programming
+# Approach 1: Brute Force
+#
+
+# Complexity Analysis
+#
+# Time complexity: O(k^2).
+# Space complexity: O(k) + O(k) ~ O(k)
+
+def get_num(row, col)
+  return 1 if row == 0 || col == 0 || row == col
+  get_num(row - 1, col - 1) + get_num(row - 1, col)
+end
+def get_row(row_index)
+  result = []
+  (row_index + 1).times do |i|
+    result.push(get_num(row_index, i))
+  end
+  result
+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]
+
+#
+# Approach 2: Dynamic Programming
 #
 
 # Complexity Analysis
@@ -51,7 +81,7 @@ def generate(num_rows)
 end
 
 #
-# Approach 2: Memory-efficient Dynamic Programming
+# Approach 3: Memory-efficient Dynamic Programming
 #
 
 # Complexity Analysis