iterate now returns a tuple of the three fractions worked on

The left, currently processed (centre) and right fractions are
returned by iterate.  This allows us to see exactly what fractions
have been generated/worked on in every iteration.

src/numerics.cpp

@@ -86,7 +86,8 @@ word_t gcd(word_t a, word_t b)
   return a;
 }
 
-Fraction iterate(std::queue<word_t> &queue, NodeAllocator &allocator)
+std::tuple<Fraction, Fraction, Fraction> iterate(std::queue<word_t> &queue,
+                                                 NodeAllocator &allocator)
 {
   if (queue.empty())
     return {};
@@ -105,10 +106,10 @@ Fraction iterate(std::queue<word_t> &queue, NodeAllocator &allocator)
   queue.pop();
   queue.push(allocator.getVal(index).left.value());
   queue.push(allocator.getVal(index).right.value());
-  node          = allocator.getVal(index);
-  Fraction best = MAX(node.value, allocator.getVal(node.left.value()).value);
-  best          = MAX(best, allocator.getVal(node.right.value()).value);
-  return best;
+  node = allocator.getVal(index);
+  // NOTE: We can be assured that left and right DO have values
+  return std::tuple(allocator.getVal(node.left.value()).value, node.value,
+                    allocator.getVal(node.right.value()).value);
 }
 
 std::string to_string(const Fraction &f)

src/numerics.hpp

@@ -22,6 +22,7 @@
 #include <optional>
 #include <queue>
 #include <string>
+#include <tuple>
 #include <vector>
 
 #define MIN(A, B) ((A) < (B) ? (A) : (B))
@@ -59,7 +60,8 @@ struct NodeAllocator
 };
 
 word_t gcd(word_t a, word_t b);
-Fraction iterate(std::queue<word_t> &queue, NodeAllocator &allocator);
+std::tuple<Fraction, Fraction, Fraction> iterate(std::queue<word_t> &queue,
+                                                 NodeAllocator &allocator);
 
 std::string to_string(const Fraction &);
 std::string to_string(const NodeAllocator &, const index_t, int depth = 1);