Problem 78

078.rb

@@ -0,0 +1,44 @@
+require 'pp'
+
+def next_m(m)
+  sign1 = (-1)**m*-1
+  term1 = m*(3*m-1)/2
+  m *= -1
+  sign2 = (-1)**m*-1
+  term = m*(3*m-1)/2
+  [
+    {sign: sign1, term: term1},
+    {sign: sign2, term: term2}
+  ]
+end
+
+m = []
+1.upto(1000) do |i|
+  sign1 = (-1)**i*-1
+  term1 = i*(3*i-1)/2
+  i *= -1
+  sign2 = (-1)**i*-1
+  term2 = i*(3*i-1)/2
+  m += [
+    {sign: sign1, term: term1},
+    {sign: sign2, term: term2}
+  ]
+end
+
+partition_answers = [1]
+partition_size = 1
+answer = 1
+while answer % 1_000_000 != 0
+  m_index = 0
+  answer = 0
+  next_term = m[m_index]
+  while next_term[:term] <= partition_size
+    answer += (partition_answers[partition_size-next_term[:term]] * next_term[:sign])
+    m_index += 1
+    next_term = m[m_index]
+  end
+  partition_answers << answer
+  partition_size += 1
+end
+
+pp partition_size-1