[W/K] :: knapsack problem

  knapsack problem
       
           Given a set of items, each with a
          cost and a value, determine the number of each item to include
          in a collection so that the total cost is less than some given
          cost and the total value is as large as possible.
       
          The 0/1 knapsack problem restricts the number of each items to
          zero or one.
       
          Such constraint satisfaction problems are often solved using
          dynamic programming.
       
          The general knapsack problem is NP-hard, and this has led to
          attempts to use it as the basis for public-key encryption
          systems.  Several such attempts failed because the knapsack
          problems they produced were in fact solvable by
          polynomial-time algorithms.
       
          [Are there any trusted knapsack-based public-key
          cryptosystems?].
       
          (1995-04-10)