Question

Suppose that you have two text files that contain sequences of integers separated by white space (blank space, tabs, and line breaks). The integers in both files appear in sorted order. with smaller values near the beginning of the file and large values closer to the end. Write a pseudocode algorithm that merges the two sequences into a single sorted sequence that is written to a third file.

Short answer

Question: Describe the process of merging two sorted integer sequences from two text files into a single sorted sequence and writing that sequence to a third file. Answer: The process involves initializing and opening the input and output files and reading the first integers from the input files. Then, while both input files have data, the algorithm compares the integers from the two files, writes the smaller one to the output file, and reads the next integer from the input file containing the smaller integer. This process continues until one of the input files is empty. After that, the remaining integers from the non-empty input file are written to the output file in order. Finally, all the files are closed.

Step-by-step solution

Initialize variables and open all files

Declare and initialize input and output file variables, namely inputFile1, inputFile2, and outputFile. Open inputFile1 and inputFile2 for reading, and open outputFile for writing.

Read integers from input files

Read the first integer from inputFile1 and inputFile2 each and store them in variables num1 and num2 respectively.

Compare and merge sorted sequences

While inputFile1 and inputFile2 are not empty, compare the integers in num1 and num2. If num1 <= num2, write num1 to outputFile and read the next integer from inputFile1, then store it in num1. If num1 > num2, write num2 to outputFile and read the next integer from inputFile2, then store it in num2. Repeat this process until either inputFile1 or inputFile2 is empty.

Write remaining integers to outputFile

When one input file becomes empty, the other input file may still have integers left. If inputFile1 still has integers, write the remaining integers from inputFile1 to outputFile in order. If inputFile2 still has integers, write the remaining integers from inputFile2 to outputFile in order.

Close all files

Once all sorted integers are written to outputFile, close inputFile1, inputFile2, and outputFile. The pseudocode for the given problem can be written as: ``` Initialize inputFile1, inputFile2, outputFile Open inputFile1 for reading Open inputFile2 for reading Open outputFile for writing Read first integer from inputFile1 into num1 Read first integer from inputFile2 into num2 While inputFile1 AND inputFile2 are not empty: If num1 <= num2: Write num1 to outputFile Read next integer from inputFile1 into num1 Else: Write num2 to outputFile Read next integer from inputFile2 into num2 While inputFile1 is not empty: Write remaining integers from inputFile1 to outputFile in order While inputFile2 is not empty: Write remaining integers from inputFile2 to outputFile in order Close inputFile1 Close inputFile2 Close outputFile ```

Key concepts

File Handling

File handling is a critical aspect of programming, especially when dealing with data that is stored outside the core program. It involves opening, reading, writing, and closing files, which allows a program to perform operations on external data.
Here's a simple breakdown of file handling:

• **Opening Files**: Before any operations can be performed, files need to be opened. This is like unlocking a door before you go in. You can open a file for reading ('r'), writing ('w'), or appending ('a').


• **Reading and Writing**: After opening, you can read data from the file or write new data into it. Reading from a file retrieves the stored information, while writing overwrites or adds new information to the file.


• **Closing Files**: Once file operations are completed, it's important to close them. This ensures that all buffers are flushed, and resources are freed.

In our case, the program opens two input files for reading the sequences of integers and an output file for writing the merged sequence. Proper file handling ensures data integrity and prevents data corruption.

Algorithm Design

Algorithm design is the process of defining a step-by-step solution to a problem that can be solved computationally. It involves structuring the problem in a manner that can be executed efficiently by the computer.

Here are some basic principles of algorithm design:

• **Clear Objectives**: Understand what the algorithm needs to achieve. Here, the objective is to merge two sorted sequences into a single sorted sequence.


• **Step-by-Step Instructions**: Break down the task into manageable steps, which makes it easier to translate into code. In the exercise above, the steps include initializing variables, reading from files, comparing numbers, writing to files, and finally closing files.


• **Efficiency**: Ensure that the algorithm performs the task in the least time possible. For merging, this involves making sure that the comparisons and writes are conducted as efficiently as possible.

Our algorithm iteratively compares elements from both sequences and writes the smaller one to the output file, ensuring the merged sequence remains sorted. This design ensures that our solution is both logical and efficient.

Merging Sorted Sequences

Merging sorted sequences is a common computational problem. The goal is to combine two sorted sequences into a single sorted sequence while maintaining the order of elements.

Let's look at the key steps involved in merging sorted sequences:

• **Initialization**: Start by reading the first element from each sequence. These elements are then compared.


• **Comparison and Writing**: The main part of the merging process involves comparing the elements from the two sequences. This is a continuous process where the smaller element is written into the output sequence, and the next element is read from the same sequence.


• **Finalizing**: When one of the sequences is exhausted (all elements have been merged), any remaining elements from the other sequence are directly appended to the merged list as they are already sorted.

By handling the data in this way, merging sorted sequences efficiently becomes similar to the merging step in the merge sort algorithm. This technique is fundamental in many sorting and data processing tasks.