CIS 315 算法讲解

CIS 315, Intermediate Algorithms
Winter 2019
Assignment 6
due Friday, March 8, 2019
1 Description
We want to devise a dynamic programming solution to the following problem: there is a string of
characters which might have been a sequence of words with all the spaces removed, and we want
to find a way, if any, in which to insert spaces that separate valid English words. For example,
theyouthevent could be from “the you the vent”, “the youth event” or “they out he vent”. If
the input is theeaglehaslande, then there’s no such way. Your task is to implement a dynamic
programming solution in one of two separate ways (both ways for extra credit):
iterative bottom-up version
recursive memoized version
Assume that the original sequence of words had no other punctuation (such as periods), no capital
letters, and no proper names - all the words will be available in a dictionary file that will be provided
to you.
Let the input string be x = x1x2...xn. We define the subproblem split(i) as that of determining
whether it is possible to correctly add spaces to xixi+1...xn. Let dict(w) be the function that will
look up a provided word in the dictionary, and return true iff the word w is in it. A recurrence
relation for split is given below:
split(i) =
true if i = n + 1
[dict(xixi+1...xj ) ∧ split(j + 1)] otherwise
Obviously, split(i) only finds out whether there’s a sequence of valid words or not. Your program
must also find at least one such sequence.
The program will read a text file from standard input. For example, if you have a Java class
named dynProg, the command java dynProg < inSample.txt is what you would use to run your
program. The name of the dictionary file should be hardwired in the code. We will be testing
your program on a file named “diction10k.txt”, and your program will be tested in a directory
containing that file. Testing will be much simpler if you can submit your program as a single file
(and not a zipped directory).
1
2 Sample Input
The first line of input is an integer C. This is followed by C lines, each containing a single string,
representing a phrase to be tested.
3
theyouthevent
theeaglehaslande
lukelucklikeslakeslukeducklikeslakeslukelucklickslakesluckducklickslakes
3 Sample Output
phrase number: 1
theyouthevent
iterative attempt:
YES, can be split
the you the vent
memoized attempt:
YES, can be split
the you the vent
phrase number: 2
theeaglehaslande
iterative attempt:
NO, cannot be split
memoized attempt:
NO, cannot be split
phrase number: 3
lukelucklikeslakeslukeducklikeslakeslukelucklickslakesluckducklickslakes
iterative attempt:
YES, can be split
luke luck likes lakes luke duck likes lakes luke luck licks lakes luck duck licks lakes
memoized attempt:
YES, can be split
luke luck likes lakes luke duck likes lakes luke luck licks lakes luck duck licks lakes
2
4 Submission
Post a copy of your Java, Python, C, or C++ program to Canvas by midnight of the due date of
Friday, March 8.