solve: Perfect Squares

Author: 0x01f7

README.md

@@ -20,7 +20,7 @@
 | 282 | [Expression Add Operators][p282]                                    | [Ruby][s282]  | Hard        |
 | 281 | [Zigzag Iterator][p281]                                             |    :lock:     | Medium      |
 | 280 | [Wiggle Sort][p280]                                                 |    :lock:     | Medium      |
-| 279 | [Perfect Squares][p279]                                             |               | Medium      |
+| 279 | [Perfect Squares][p279]                                             | [Ruby][s279]  | Medium      |
 | 278 | [First Bad Version][p278]                                           | [Ruby][s278]  | Easy        |
 | 277 | [Find the Celebrity][p277]                                          |    :lock:     | Medium      |
 | 276 | [Paint Fence][p276]                                                 |    :lock:     | Easy        |

algorithms/perfect_squares.rb

@@ -0,0 +1,36 @@
+# https://leetcode.com/problems/perfect-squares/
+#
+# Given a positive integer n, find the least number of perfect square
+# numbers (for example, 1, 4, 9, 16, ...) which sum to n.
+#
+# For example,
+#
+#     given n = 12, return 3 because 12 = 4 + 4 + 4;
+#     given n = 13, return 2 because 13 = 4 + 9.
+
+
+# @param {Integer} n
+# @return {Integer}
+def num_squares(n)
+  s = Math.sqrt(n).truncate
+  return 1 if n == s * s
+
+  v = Array(1..s).map { |num| num * num }
+  q, l = [n], 1
+
+  while true
+    newq = []
+
+    q.each do |n1|
+      v.each do |n2|
+        case n1 <=> n2
+        when  1; newq << n1 - n2
+        when  0; return l
+        when -1; break
+        end
+      end
+    end
+
+    q, l = newq.uniq, l + 1
+  end
+end