# What Are Euler Circuits in Data Structure?

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Angela Bailey

An Euler circuit is a path in a graph that visits every edge exactly once and returns to the starting vertex. In other words, it is a closed walk that covers all the edges of the graph without repeating any of them.

## Characteristics of Euler Circuits

Euler circuits have some key characteristics that make them unique:

• Connected Graph: The graph must be connected, meaning there is a path between any two vertices.
• Eulerian Graph: The graph must be Eulerian, which means that all vertices have an even degree.

## Finding Euler Circuits

To find an Euler circuit in a graph, we can use Hierholzer’s algorithm. This algorithm follows these steps:

1. Select a Starting Vertex: Choose any vertex as the starting point for the circuit.
2. Create Subcircuits: Traverse each edge only once and return to the starting vertex to form subcircuits.
3. Combine Subcircuits: Combine all subcircuits into one single Euler circuit by merging them at common vertices.

### An Example

Let’s consider a simple example to understand how an Euler circuit works. We have the following graph:

```      A --- B
/ \   /
/   \ /
C --- D
```

This graph is connected and all vertices have an even degree. Therefore, it satisfies the conditions for having an Euler circuit.

We can start from vertex A and follow these steps:

1. A – B – D – C – A: Start from vertex A, traverse edges AB, BD, DC, and return to A.

Thus, the Euler circuit for this graph is A – B – D – C – A.

## Applications of Euler Circuits

Euler circuits have various applications in computer science and real-life scenarios:

• Network Routing: Euler circuits can be used to find the most efficient route for data packets in network routing algorithms.
• Tour Planning: In tourism planning, Euler circuits can help identify the optimal path to visit multiple destinations without repeating any.
• Circuit Board Testing: In circuit board testing, Euler circuits are used to ensure that all connections on the board are functioning correctly.

In conclusion, an Euler circuit is a closed walk that covers all edges of a graph without repeating any. It has specific characteristics and can be found using Hierholzer’s algorithm. Understanding Euler circuits is essential for solving various graph-related problems in data structures and algorithms.