Source: 📖 Problem Solving with Algorithms and Data Structures using Python ch8.15

What is a depth first search?

Like breadth first search (DFS), depth first search (DFS) is an algorithm for searching graphs and graph-like structures (such as trees). Both algorithms will take a starting node/vertex, and build a search tree that spans out from this node at its root. Where they differ is that a BFS algorithm visits all immediate neighbour/child nodes before moving on, thereby building the resulting search tree one level at a time, whereas DFS builds the search tree one branch at a time by recursively visiting the first available neighbour/child node until there are no more available connections to explore, then backtracking its path until it returns to a node that has other unvisited neighbours/children, where the process continues the same way (one branch at a time).