What Do You Mean by Disjoint Set Data Structure?


Scott Campbell

A disjoint set data structure, also known as a union-find data structure, is a powerful tool used in computer science to efficiently manage a partitioning of elements into disjoint sets. It provides fast operations for determining whether two elements belong to the same set, merging two sets together, and finding the representative element of a set.

Representing Sets

Each set in a disjoint set data structure is represented by a tree-like structure. In this representation, each element in the set points to its parent node. The root of each tree denotes the representative element of its corresponding set.

Initially, each element is considered to be in its own separate set. Therefore, each element’s parent pointer points to itself. This way, we can determine if an element is the representative by checking if its parent points to itself.


The disjoint set data structure supports three main operations: Find, Union, and CreateSet.


  • To determine which set an element belongs to, we follow the parent pointers until we reach an element whose parent points to itself (i.e., the root).
  • The root represents the entire set and can be used as the representative for that particular set.
  • This operation has a time complexity of O(log n), where n is the number of elements.


  • The union operation merges two sets together by making one of them a subset of the other.
  • To perform this operation efficiently, we first find the representatives (roots) of both sets using the Find operation.
  • We then make one of the roots the parent of the other root, effectively merging the two sets together.


  • The create set operation initializes a new set with a single element.
  • This operation is typically performed when adding a new element to the disjoint set data structure.
  • It has a time complexity of O(1).


The disjoint set data structure finds applications in various algorithms and problems, including:

  • Kruskal’s algorithm for finding the minimum spanning tree of a graph.
  • Connected components in an undirected graph.
  • Image processing algorithms, such as image segmentation and region labeling.
  • Social network analysis, where it can be used to find communities or clusters within a network.

The efficiency of the disjoint set data structure makes it an essential tool in solving these problems and more. By properly implementing and utilizing it, you can optimize your algorithms and improve their performance.


In summary, a disjoint set data structure provides an efficient way to manage partitioning of elements into sets. With its support for quick find, union, and create set operations, it proves to be invaluable in various applications. By understanding its underlying principles and correctly implementing it, you can leverage this powerful tool to solve complex problems effectively.

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