frobnitzem

// Solve the knapsack problem using recursive descent.
// This wraps the actual solver below with a nice interface.
// It also handles non-integer cost, but then the complexity
// scales with the precision of the cost!
//
// obj is an object of named [cost, benefit] pairs, e.g.
// { banana: [5, 33],
//   apple:  [1, 12],
//   kiwi:   [1, 7]
// }