Dijkstra's algorithm is commonly employed in routing systems to calculate the shortest route between locations. It helps find the most efficient path in networks, such as road maps or computer networks.

Merge Sort would be the preferred choice in this scenario. It is a stable sorting algorithm, meaning it preserves the relative order of elements with equal keys. Additionally, its time complexity of O(n log n) ensures efficient sorting, making it suitable for stable sorting tasks.

For a plagiarism detection system in a large document database, the Rabin-Karp algorithm would be a suitable choice. It utilizes hashing to efficiently detect patterns, making it well-suited for identifying similarities in documents by comparing hash values.

The Ford-Fulkerson algorithm aims to solve the maximum flow problem in a network, where the goal is to find the maximum amount of flow that can be sent from a designated source to a designated sink in a flow network.

The worst-case time complexity of the selection sort algorithm is O(n^2), where 'n' is the number of elements in the array. This is due to the nested loops used to find the minimum element in each iteration.

In a scenario with an unsorted list that is constantly changing, linear search has the advantage of simplicity. However, its time complexity of O(n) may lead to inefficiency as the list size grows. Advantages include ease of implementation, but disadvantages involve potentially slower performance compared to other algorithms like hashing or jump search, which can exploit certain characteristics of the data for faster retrieval.

It ensures finding the shortest path by maintaining a priority queue that contains the shortest distance to each node from the source. The priority queue helps prioritize nodes based on their distance values, facilitating efficient path exploration.

Regular expressions can indeed be used to validate email addresses. The pattern can be crafted to ensure the presence of a valid username, domain, and top-level domain (TLD), adhering to the typical structure of email addresses.

Red-black trees provide strict guarantees on the height of the tree. These guarantees ensure that the height of the tree is logarithmic in the number of nodes, leading to efficient search, insertion, and deletion operations.

In a graph containing cycles, topological sorting cannot be performed as it violates the prerequisite of a directed acyclic graph (DAG). Topological sorting relies on establishing a linear ordering of vertices, which is not possible in the presence of cycles.