**What is Kruskal Algorithm?**

- Kruskal’s algorithm for finding the Minimum Spanning Tree(MST), which finds an edge of the least possible weight that connects any two trees in the forest
- It is a greedy algorithm.
- It finds a subset of the edges that forms a tree that includes every vertex, where the total weight of all the edges in the tree is minimized.
- If the graph is not connected, then it finds a minimum spanning forest (a minimum spanning tree for each connected component).
- Number of edges in MST: V-1 (V – no of vertices in Graph).

**Example**:

**How this algorithm works?**

We strongly recommend reading Find Cycle in Undirected Graph using Disjoint Set (Union-Find) before continue.

- Sort the edges in ascending order of weights.
- Pick the edge with the least weight. Check if including this edge in spanning tree will form a cycle is Yes then ignore it if No then add it to spanning tree.
- Repeat the step 2 till spanning tree has V-1 (V – no of vertices in Graph).
- Spanning tree with least weight will be formed, called Minimum Spanning Tree

**Pseudo Code:**

KRUSKAL(G): A = ∅ foreach v ∈ G.V: MAKE-SET(v) foreach (u, v) in G.E ordered by weight(u, v), increasing: if FIND-SET(u) ≠ FIND-SET(v): A = A ∪ {(u, v)} UNION(u, v) return A

See the animation below for more understanding.

**JavaCode:**

**Output:**

Minimum Spanning Tree: Edge-0 source: 1 destination: 2 weight: 1 Edge-1 source: 1 destination: 3 weight: 2 Edge-2 source: 3 destination: 4 weight: 2 Edge-3 source: 0 destination: 2 weight: 3 Edge-4 source: 4 destination: 5 weight: 6

Click here to read about – Minimum Spanning Tree using Prim’s Algorithm

Reference – Wiki