Implementation of mergesort

Requirements:

Write a program to read an input sequence and then produce an array of links giving the values in ascending order. The first line of the input file is the length of the sequence (n) and each of the remaining n lines is a non-negative integer. The first line of the output indicates the subscript of the smallest input value. Each of the remaining output lines is a triple consisting of a subscript along with the corresponding input sequence and link values.

Getting Started:

1. Your program should read the input files by using Unix shell redirection (e.g. a.out<lab1.dat) to read the input from

stdin (C). By using redirection, it is unnecessary to explicitly open and close the input file, nor should your program

prompt for a file name. You should dynamically allocate tables for storing the input keys and the table of links. Unlike

the mergesort in Notes 1 and CLRS, the table of keys is never modified.

2. The link values are not initialized before the recursive mergesort begins. Each link will be initialized to -1 when its

sequence value is placed in a single-element list (at the bottom of the recursion’s “tree”).

3. The input sequence array and the link array may be global. Under this assumption, the following prototype may be used:

int mergeSort(int start,int count) where start is the first subscript for a subarray of count elements. The returned int is the subscript of the first element in the resulting sorted sublist. The last element in the sublist will have a link value of -1.

4. The critical part of the code is a linear-time merge of two subarrays that previously had their link values set for ordered

sublists. (Be sure to understand the merging concept from pp. 3-4 of Notes 1 before proceeding.) The merge will revise

the link values to give a single ordered list.

5. If an input value appears more than once, those elements should be ordered by subscripts in the final list, i.e. your sort

code will be stable.

Consider the following input file:

8

5

5

2

4

3

1

0

1

The output (as subscript/value/link triples) will be:

First element is at subscript 6

0 5 1

1 5-1

2 2 4

3 4 0

4 3 3

5 1 7

6 0 5

7 1 2

Notice that the input sequence ordering has not changed.