In this paper we propose a new method for deriving a practical linear-time algorithm from the specification of a maximum-weight sum problem: From the elements of a data structure x, find a subset which satisfies a certain property p and whose weightsum is maximum. Previously proposed methods for automatically generating linear-time algorithms are theoretically appealing, but the algorithms generated are hardly useful in practice due to a huge constant factor for space and time. The key points of our approach are to express the property p by a recursive boolean function over the structure x rather than a usual logical predicate and to apply program transformation techniques to reduce the constant factor. We present an optimization theorem, give a calculational strategy for applying the theorem, and demonstrate the effectiveness of our approach through several nontrivial examples which would be difficult to deal with when using the methods previously available.

In existing work on graph algorithms, it is known that a linear time algorithm can be derived mechanically from a logical formula for a class of optimization problems. But this has a serious problem that the derived algorithm has huge constant factor. In this work, we redene this problem on recursive data structures as a maximum marking problem and propose method for deriving a linear time algorithm for that. In this method, speci cation is given using recursive functions instead of logical formula, which results in a practical linear time algorithm. This method is mechanical and in fact, based on this deriving method, we make a system which automatically generates a practical linear time algorithm from specication for a maximum marking problem.

In this paper, we propose a new method to derive practical linear time algorithms for maximum weightsum problems. A maximum weightsum problem is specified as follows: given a recursive data x, find an optimal subset of elements of x which not only satisfies certain property p but also maximizes the sum of the weight of elements of the subset. The key point of our approach is to describe the property p as a functional program. This enables us to use program transformation techniques. Based on this approach, we present the optimization theorem, with which we construct a systematic framework to calculate efficient linear time algorithms for maximum weightsum problems on recursive data structures. We demonstrate effectiveness of our approach through several interesting and non-trivial examples, which would be difficult to solve by known approaches.