dynamic-connectivity.md

Dynamic Connectivity

Dynamic Connectivity

Given a set of N objects.

• Union command: connect two objects.
• Find/connected query: is there a path connecting the two objects?

Modelling the Connections

We assume "is connected to" is an equivalence relation:

• Reflexive: p is connected to p.
• Symmetric: if p is connected to q, then q is connected to p.
• Transitive: if p is connected to q and q is connected to r, then p is connected to

Connected components: Maximal set of objects that are mutually connected.

Implementing Operations

Find Query: Check if two objects are in the same component.

Union command: Replace components containing two objects with their union.

Union Find Data Type - Java

public class UF {

    // initialize union-find data structure with N objects (0 to N – 1)
    UF(int N);
    
    // add connection between p and q
    void union(int p, int q);
    
    // are p and q in the same component?
    boolean connected(int p, int q);
    
    // component identifier for p (0 to N – 1)
    int find(int p);
    
    // number of components
    int count();
}