What is an alarm clock algorithm?

The alarm clock algorithm escalates the breadth-first search (BFS) by skipping the dummy nodes or reducing the time spent on unnecessary nodes. In this Answer, we will explain the alarm clock algorithm by considering the below-illustrated graph.

Steps to implement an alarm clock algorithm

The main steps of this algorithm are mentioned below.

1. The starting node is denoted $S$ as shown in the graph. The alarm clock of the start node is set at $T = 0$. Here, $T$ represents time.

2. Repeat the following steps until there is no more alarm.

   1. Let the next alarm go off at time $T$ for dummy node $d$ , which means that we have reached at $d$ at distance $T$ from the starting node.

   2. For each neighbor of a node$d$ in the original graph $G$:

      1. If there is no alarm set for node $n$ yet, set the alarm for time $T + l(d,n)$, where $l(d,n)$is the edge length between nodes $d$ and $n$.

      2. If an alarm is already set for a node $n$ compare its current time with $T + l(d,n)$. If the current alarm is set for a later time, update it to the earlier time $T + l(d,n)$.

In the alarm clock algorithms, the primary purpose is to wake up the algorithm whenever it reaches an actual node. This process will allow us to reduce time and skip dummy nodes present in the graph $G'$. The algorithm will set the time for each node, as explained above.

Explanation

In the graph $G'$, the BFS algorithm progresses through the first $89$ minutes, exploring dummy nodes $S-X$ and $S-Y$. Alarms are set for nodes $X$ and $Y$ at times $90$ and $300$, respectively. Suppose that at every minute, the algorithms pass only one dummy node.

When the alarm for node $X$ goes off at $T = 90$, the algorithm will find the node $X$. As it finds the node $X$, the estimated arrival time for node $Y$ will be adjusted to $T=130$. This is because there is a path from $S-X-Y$ that has the minimum distance from $S-Y$.

This ensures that whenever the algorithm finds the actual node, the alarm will beep, and the path for the graph will be updated accordingly.

Advantages

There are several advantages of using an alarm clock algorithm, some of which are given below:

• BFS takes a lot of time while traversing through a graph. With the help of the alarm clock algorithm, we can pass through dummy nodes by setting the alarm to snooze, but when we encounter an actual node, we set the alarm to wake up.

• The main advantage of using the alarm clock algorithm is finding the shortest path from one node to the other.

Conclusion

In this Answer, we learned how to find the shortest path with the help of the alarm clock algorithm. This algorithm helps us in finding the most efficient path between the nodes of the graph. Also, we use it to calculate the distances with the positive edge length. Hopefully, with the help of this Answer, you will have a better grasp of the alarm clock algorithm. Therefore, it is time to solve a quick quiz.