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CS 435, Online Programming Assignment 3 Dr. David Nassimi

Algorithms Sorting Strings LSD

This assignment is to alphabetically sort n strings, each with maximum-length of k = 21 characters. (Youmay assume n 1000.) The algorithm to be used is LSD (Least-Significant-Digit-First) radixsort. Thealgorithm must run in O(n) time, where one character operation takes one unit of time. You must handlethe strings on a character-by-character basis, one character at a time. (Each character operation takesO(1) time.)

The strings consist of only upper-case letters A-Z, with no space. The strings need not be distinct. (Forexample, there may be several PATEL in a class list!)

Each string has at most k characters. Shorter strings must be padded with blank characters (as they areread from a file) to reach the fixed length of k.

First, read the strings from a text file “f.txt”. Assume that each string starts at the beginning of a newline and ends with one or more white-space-characters. (An end-of-line character is a white-space.) Storethe strings in a two-dimesional array S with n rows and k columns. That is, string i is stored in S[i, 1..k].

For efficiency, once the strings have been read into array S, they must stay in that order and not be movedduring the sorting. Instead, we use a pointer array (array of string indices) P[0..n1]. Initially, set P[i] = ifor all i. During the sorting, we move these indices. At the end of sorting, P[0] will be the index of thestring which is the first in the sorted order, P[1] the second string in the sorted order, and so on.

At the end, output the strings in sorted order to a text file “g.txt”. Use the same format as the input file,with each string as one line. (Each string must begin at the beginning of a line and end with an end-of-linecharacter.)

Notes on naming files: For ease of grading, your program must receive the names of input-file andoutput-file from the command line. And these file names must have default names “f.txt” and “g.txt”,respectively. Then the user will be able to either specify a file name, or decide to go with the default name.

That is, your program will first receive the name of input file.

Please specify the input file (default = f.txt ):

After receiving the name of input file, your program will then receive the name of output file.

Please specify the output file (default = g.txt):

Make sure you adhere strictly to this protocal so the TA will be able to easily specify his/her own file nameto run your program.


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