Depth First Search in java

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If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.


In previous post, we have seen breadth-first search(bfs). In this post, we will see how to implement depth-first search(DFS) in java.

Graph traversal Algorithms

In DFS,  You start with  an un-visited node and start picking an adjacent node, until you have no choice, then you backtrack until you have another choice to pick a node, if not, you select another un-visited node.

DFS can be implemented in two ways.

  • Recursive
  • Iterative

Iterative

Depth-first search can be implemented using iterative approach.
Let see with the help of example:

Depth first search example

We start with node 40. It then visits node 20, node 50, node 70 respectively as they are directly connected. After that, it backtracks to node 20 and visited node 60, node 30 and node 10 respectively.

Recursive

Depth first search can be implemented using recursion too. We do not need to maintain external stack, it will be taken care by recursion.

Java DFS Example

There are two ways to represent a graph.

    • Using Neighbours list
    • Using Adjacency Matrix

Using Neighbours list

In this, you can have List<Node> as neighbours in Node class as below.

Here is the complete java program for DFS implementation for iterative as well as recursive method.

When you run above program, you will get below output

Using Adjacency Matrix

Adjacency_matrix is used to find the connection between two nodes.

if adjacency_matrix[i][j]==1, then nodes at index i and index j are connected

Below diagram will help you to understand adjacency matrix.

Adjacency Matrix

Create DepthFirstSearchExample.java

When you run above program, you will get below output

Please go through data structure and algorithm interview programs for more such programs.

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