Given a sorted Alien dictionary, find order of characters
In an alien language, surprisingly, they also use English lowercase letters, but possibly in a different order. The order of the alphabet is some permutation of lowercase letters.
Category: Graphs
Topological Sort [Hackerearth]
A Topological sort of a Directed-Acyclic graph G is a linear ordering of all its vertices such that if G contains an edge E (u, v), then u appears before v in the ordering. And if the graph is not acyclic, then no linear ordering is possible.
DFS (Depth-First Search) in Binary Trees and Graphs
DFS (Depth-First Search) is an algorithm for traversing a graph. DFS starts from source vertex (graph) or root (in trees) and then visits an unvisited adjacent node v. After that it checks if node v has any adjacent node which is unvisited. If it reaches a leaf node or any node having no unvisited adjacent node. It backtracks and continue traversing other nodes.
BFS (Breadth-First Search) in Binary Trees and Graphs
BFS (Breadth-First Search) is one of the simplest algorithms for traversing a graph. Prim’s min-spanning-tree and Djikstra’s algorithm use similar ideas as BFS. BFS is also known as Level-order traversal because the algorithm discover all nodes at distance k from root before discovering any nodes at distance k+1.