A Collection of Code Snippets in as Many Programming Languages as Possible

This project is maintained by TheRenegadeCoder

Welcome to the Depth First Search page! Here, you'll find a description of the project as well as a list of sample programs written in various languages.

This article was written by:

- Jeremy Grifski
- rzuckerm

Depth first search is a type of graph search algorithm. It is often used on trees (which are special types of graphs). It takes linear time to traverse a graph and find a given vertex, specifically O(num_vertices + num_edges). This search algorithm is often used by web crawlers or in machine learning tasks. There, the graph that should be traversed is often too big to be do it in a single run. In such cases, the algorithm can be limited in different ways, for example by limiting depth or visited nodes.

The algorithm traverses the graph one node after the other, but takes priority in going deeper into the graph opposed to going broader first. This means, that it visits further children of children before visiting potential siblings of them.

For the purposes of this project, we'll assume that the search space is a tree represented as an adjacency matrix together with a list of the vertex values in the tree. Specifically, we'll accept three inputs on the command line: the tree adjacency matrix, the list of vertex values (as integers) and the vertex value to find:

```
./depth-first-search.lang "0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0" "2, 3, 6, 77, 44, 46, 1, 321, 5" "5"
```

Here we've chosen to represent the graph as a serialized list of integers. Since the input string represents a square matrix, we should be able to take the square root of the length to determine where the rows are in the string. In this case, we have 81 values, so we must have 9 nodes. If we reformat the input string as a matrix, we'll notice that the values in the matrix represent the edges between vertices. Taking the vertex values into account as well, the resulting matrix could look something like the following:

Mapping | 2 | 3 | 6 | 77 | 44 | 46 | 1 | 321 | 5 |
---|---|---|---|---|---|---|---|---|---|

2 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |

3 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 |

6 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 |

77 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |

44 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |

46 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |

1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |

321 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |

5 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |

This matrix will result in a tree that looks like this:

```
2
/ | \
3 6 77
/ | / \ \
44 46 1 321 5
```

If successful, the script should return `true`

. Otherwise, the script should return `false`

.
If any user input errors occur, the script should output the following usage message:
`Usage: please provide a tree in an adjacency matrix form ("0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0") together with a list of vertex values ("1, 3, 5, 2, 4") and the integer to find ("4")`

.

Every project in the Sample Programs repo should be tested. In this section, we specify the set of tests specific to Depth First Search. In order to keep things simple, we split up the testing as follows:

- Depth First Search Valid Tests
- Depth First Search Invalid Tests

Description | Tree Input | Vertex Values | Target Integer Input | Output |
---|---|---|---|---|

Sample Input: First True | "0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0" | "1, 3, 5, 2, 4" | "1" | "true" |

Sample Input: Last True | "0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0" | "1, 3, 5, 2, 4" | "4" | "true" |

Sample Input: Middle True | "0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0" | "1, 3, 5, 2, 4" | "5" | "true" |

Sample Input: One True | "0" | "1" | "1" | "true" |

Sample Input: One False | "0" | "1" | "6" | "false" |

Sample Input: Many False | "0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0" | "1, 3, 5, 2, 4" | "7" | "false" |

Description | Tree Input | Vertex Values | Target Integer Input |
---|---|---|---|

No Input | |||

Missing Input: Tree | "" | "1, 3, 5, 2, 4" | "4" |

Missing Input: Vertex Values | "0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0" | "" | "1" |

Missing Input: Target | "0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0" | "1, 3, 5, 2, 4" | "" |

All of these tests should output the following:

```
Usage: please provide a tree in an adjacency matrix form ("0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0") together with a list of vertex values ("1, 3, 5, 2, 4") and the integer to find ("4")
```

There are 10 articles:

- Depth First Search in Algol68
- Depth First Search in Beef
- Depth First Search in C++
- Depth First Search in Commodore Basic
- Depth First Search in Euphoria
- Depth First Search in Java
- Depth First Search in Mathematica
- Depth First Search in Php
- Depth First Search in Python
- Depth First Search in Rust