Problem 82

082.rb

@@ -0,0 +1,46 @@
+require 'pp'
+
+matrix = Array.new
+
+rows = IO.readlines('matrix_82.txt')
+rows.each_with_index do |row, index|
+  matrix[index] = row.split(',').map(&:to_i)
+end
+
+# matrix = [
+#   [131, 673, 234, 103, 18],
+#   [201, 96, 342, 965, 150],
+#   [630, 803, 746, 422, 111],
+#   [537, 699, 497, 121, 956],
+#   [805, 732, 524, 37, 331]
+# ]
+
+matrix_answers = []
+0.upto(matrix.size-1) do |i|
+  row = Array.new(matrix.size)
+  row[matrix.size-1] = matrix[i][matrix.size-1]
+  matrix_answers << row
+end
+
+(matrix.size-2).downto(0) do |col|
+  (matrix.size-1).downto(0) do |row|
+    starting_number = matrix[row][col]
+    options = [starting_number + matrix_answers[row][col+1]]
+
+    down_total = starting_number
+    (row-1).downto(0) do |down_row|
+      down_total += matrix[down_row][col]
+      options << (down_total + matrix_answers[down_row][col+1])
+    end
+
+    up_total = starting_number
+    (row+1).upto(matrix.size-1) do |up_row|
+      up_total += matrix[up_row][col]
+      options << (up_total + matrix_answers[up_row][col+1])
+    end
+
+    matrix_answers[row][col] = options.min
+  end
+end
+
+pp matrix_answers.map{|m| m[0]}.min