Question

Write an algorithm to read in a sequence of values \(V \geq 0\), one at a time, and determine if the list contains at least one adjacent pair of values that are identical. The end of the entire list is marked by the special value \(V=-1\). For example, if you were given the following input: \(14,3,7,7,9,1,804,22,-1\) the output of your algorithm should be a 'Yes' because there is at least one pair of adjacent numbers that are equal (the 7s). However, given the following input: \(14,3,7,77,9,1,804,22,-1\) the output of your algorithm should be a 'No' because there are no adjacent pairs that are

Short answer

Check adjacent values; output 'Yes' for a match or 'No' if none.

Step-by-step solution

Initialize Variables

Begin by setting up two variables to store the current and previous values. Assign a placeholder value to `previous_value` (e.g., -2) since -1 is the end marker and any number >= 0 is considered a valid input.

Read Input

Continuously read each value in the sequence from the input. This can be achieved using a loop that continues until the special end marker (-1) is detected.

Check for End Marker

Inside the loop, check if the current value is -1. If it is, break out of the loop since it marks the end of input.

Compare Values

Compare the current value with `previous_value`. If they are equal, print 'Yes' and exit the loop or function since we found an adjacent pair.

Update Previous Value

If the current value is not -1 and does not match `previous_value`, update `previous_value` to be the current value, and continue reading the next input.

End of Input

If the loop completes without finding any equal adjacent pairs, print 'No' as the output.

Key concepts

Adjacent Values

Adjacent values in a sequence refer to two elements positioned next to each other in a list. These values are crucial when you're tasked with finding pairs that meet specific criteria, like being equal. In the context of our problem, the challenge is to determine if there are any such equally adjacent pairs within a sequence.

Identifying adjacent values requires stepping through a list while holding onto the current and previous elements for comparison. When these two values are equal, you've identified an adjacent pair.

Key points to consider include:

• The concept of adjacency focuses on neighboring elements.
• Comparing each element with the one before it is crucial for spotting these pairs.
• In cases where at least one pair of adjacent values is equal, the solution yields 'Yes'. Otherwise, it outputs 'No'.

Sequence Processing

Sequence processing involves handling a series of elements in a defined order. This process is fundamental when developing algorithms to analyze sequences like those described in our exercise.

To process the sequence effectively:

• We use loops to iterate over all elements until reaching a stopping condition, in this case, a special marker (-1).
• During iteration, each element is examined one after another, facilitating operations such as comparisons and updates.
• Sequence processing is what aids in keeping track of order and context, both vital for determining adjacent equal values.

In our problem, sequence processing allows us to check each number against its predecessor efficiently. By methodically moving through the sequence, we maintain a reliable process to find the desired output.

Input Validation

Input validation is the practice of ensuring data meets certain requirements before processing it. In algorithms, it's a vital step to prevent errors and ensure the program runs smoothly.

For our exercise, input validation is subtly handled:

• First, by employing a loop that operates until it encounters a termination marker (-1), we inherently filter out invalid end conditions during processing.
• By using a reserved initial value for comparisons, we avoid false triggers with end markers or invalid input like negative numbers other than -1.
• The focus of input validation is to ensure that only non-negative numbers, and a special end marker, are processed.

Effective input validation not only ensures the integrity of the sequence but also provides a clear stopping point, making the algorithm predictable and avoiding unnecessary computation once the end is reached. This step completes the robust cycle from input to validated processing, leading to accurate output.