118. Pascal's Triangle (#120)

Author: remy727

README.md

@@ -91,6 +91,7 @@
 | 113 | Path Sum II | [Ruby](./algorithms/ruby/0113-path-sum-ii.rb) | Medium |
 | 114 | Flatten Binary Tree to Linked List | [Ruby](./algorithms/ruby/0114-flatten-binary-tree-to-linked-list.rb) | Medium |
 | 117 | Populating Next Right Pointers in Each Node II | [Ruby](./algorithms/ruby/0117-populating-next-right-pointers-in-each-node-ii.rb) | Medium |
+| 118 | Pascal's Triangle | [Ruby](./algorithms/ruby/0118-pascals-triangle.rb) | Easy |
 | 120 | Triangle | [Ruby](./algorithms/ruby/0120-triangle.rb) | Medium |
 | 121 | Best Time to Buy and Sell Stock | [Ruby](./algorithms/ruby/0121-best-time-to-buy-and-sell-stock.rb) | Easy |
 | 122 | Best Time to Buy and Sell Stock II | [Ruby](./algorithms/ruby/0122-best-time-to-buy-and-sell-stock-ii.rb) | Medium |

algorithms/ruby/0118-pascals-triangle.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+# 118. Pascal's Triangle
+# Easy
+# https://leetcode.com/problems/pascals-triangle
+
+=begin
+Given an integer numRows, return the first numRows of Pascal's triangle.
+In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:
+
+Example 1:
+Input: numRows = 5
+Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
+
+Example 2:
+Input: numRows = 1
+Output: [[1]]
+
+Constraints:
+* 1 <= numRows <= 30
+=end
+
+# @param {Integer} num_rows
+# @return {Integer[][]}
+def generate(num_rows)
+  result = [[1]]
+
+  (num_rows - 1).times do
+    prev_row = result.last
+    row = [1]
+
+    0.upto(prev_row.size - 2) do |i|
+      row << prev_row[i] + prev_row[i + 1]
+    end
+
+    row << 1
+    result << row
+  end
+
+  result
+end
+
+# **************** #
+#       TEST       #
+# **************** #
+
+require "test/unit"
+class Test_generate < Test::Unit::TestCase
+  def test_
+    assert_equal [[1], [1, 1], [1, 2, 1], [1, 3, 3, 1], [1, 4, 6, 4, 1]], generate(5)
+    assert_equal [[1]], generate(1)
+  end
+end