3106	 A Fast Algorithm for Copying List Structures	 An algorithm is presented for copying an arbitrarily linked list structure into a block of contiguous storage locations without destroying the original list. Apart from a fixed number of program variables no auxiliary storage such as a stack is used. The algorithm needs no mark bits and operates in linear time. It is shown to be significantly faster than Fisher s algorithm the fastest previous linear-time algorithm for the same problem. Its speed comes mainly from its efficient list-traversal technique which folds the processing stack into the structure being built and from its classification of list cells into nine types which enables processing operations to be optimized for each type. List copying Lisp space complexity constant workspace
