What Data Structure Can Be Used to Implement Disjoint Sets?


Scott Campbell

When it comes to implementing disjoint sets, there are several data structures that can be used. Each data structure has its own advantages and trade-offs, so it’s important to choose the right one based on the specific requirements of your application.

Array-Based Implementation

One of the simplest ways to implement disjoint sets is by using an array-based approach. In this approach, each element in the array represents a set, and the value stored in each element points to its parent set. The root of a set can be identified by a negative value or by pointing to itself.

To perform operations like union and find, we can use simple array manipulations. Union operation involves finding the roots of two sets and making one of them a child of the other. Find operation involves traversing the parent pointers until we reach a root.


  • Simplicity: Array-based implementation is easy to understand and implement.
  • Ease of Union: The union operation in this approach is quite efficient as it only requires changing a few pointers.


  • Inefficient Find Operation: Finding the root of a set in an array-based implementation can be slow if the tree becomes unbalanced.
  • Limited Scalability: This approach has limited scalability as it requires pre-allocating memory for a fixed number of elements.

Tree-Based Implementation

The tree-based implementation uses trees or forests to represent disjoint sets. Each tree represents a set, with each node pointing to its parent. The root node represents the set itself.

There are several variations of tree-based implementations, such as rank-based and path compression. In the rank-based approach, we always make the smaller tree a child of the larger tree during union operations.

This helps to keep the trees balanced and improves the efficiency of find operations. Path compression involves updating the parent pointers while traversing them during find operations, which further improves performance.


  • Efficient Find Operation: Tree-based implementations provide efficient find operations, especially when combined with path compression.
  • Better Scalability: Unlike array-based implementations, tree-based approaches can handle dynamic sets without requiring pre-allocation of memory.


  • Inefficient Union Operation: The union operation in a basic tree-based implementation can be slow if trees become unbalanced.
  • Potential for Unbalanced Trees: Without proper balancing techniques like rank-based union, trees can become unbalanced over time.

Balanced Tree-Based Implementation

To overcome the limitations of basic tree-based implementations, balanced tree data structures like AVL trees or red-black trees can be used. These data structures ensure that the height of the trees remains balanced, leading to efficient union and find operations.

The basic idea is to represent each set as a node in a balanced binary search tree. Each node contains information about its parent, left child, right child, and other attributes specific to balancing techniques used by the data structure. Union and find operations can be performed by manipulating these attributes according to the rules defined by the balancing technique.


  • Efficient Operations: Balanced tree-based implementations provide efficient union and find operations due to their balanced nature.
  • Dynamic Scalability: These implementations can handle dynamic sets without requiring pre-allocation of memory.


  • Complexity: Balanced tree-based implementations are more complex to understand and implement compared to array-based or basic tree-based approaches.
  • Higher Memory Overhead: These implementations require additional memory to store the attributes required for balancing.

In conclusion, there are several data structures that can be used to implement disjoint sets. Each approach has its own advantages and trade-offs, so it’s important to choose the right one based on the specific requirements of your application.

Array-based implementation provides simplicity but may suffer from efficiency and scalability issues. Tree-based implementations offer better efficiency and scalability, especially when combined with balancing techniques like rank-based union and path compression. Finally, balanced tree-based implementations provide efficient operations but come with increased complexity and higher memory overhead.

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