Bidirectional Search

Definition of Bidirectional Search

Bidirectional search is a search algorithm in which the search is conducted simultaneously from the initial state and the goal state, progressing toward each other. The primary aim of this technique is to significantly reduce the search time and computational complexity. Once the two searches meet, a solution is constructed by connecting the common point from both search paths.


The phonetic pronunciation of “Bidirectional Search” is:bih-dahy-rek-shuh-nuhl surch

Key Takeaways

  1. Bidirectional search is an advanced searching technique that starts the search from both the source node and the target node simultaneously, effectively following a forward search from the source node and a backward search from the target node.
  2. This search algorithm is often faster and more efficient than unidirectional search methods like breadth-first and depth-first search, as it reduces the number of search layers that need to be explored, especially in complex networks and large graphs.
  3. However, bidirectional search problems can be more complicated to implement and may require additional memory compared to their unidirectional counterparts, since they must maintain and update two separate search trees or queues.

Importance of Bidirectional Search

Bidirectional search is an important technology term because it greatly enhances search efficiency in various applications, such as artificial intelligence, navigation, and problem-solving domains.

It is a search algorithm that works simultaneously from both the initial state and the goal state, expanding search trees from both ends.

As these trees progress in their respective directions, they eventually converge, leading to the discovery of an optimal or near-optimal solution.

By simultaneously exploring the search space from both ends, bidirectional search significantly reduces the search time and resources required, thereby improving the performance of the system that employs it.


Bidirectional search is a powerful problem-solving technique that aims to significantly reduce the time and computational effort required to find optimum solutions in various search and pathfinding problems. The primary purpose of this search strategy is to enhance efficiency and reduce the search space compared to traditional approaches such as depth-first, breadth-first, or Dijkstra’s algorithm.

It is particularly useful in scenarios where finding the shortest path or the most effective choice among numerous possibilities is essential, such as in route planning, artificial intelligence, and game solving. The core idea behind bidirectional search is to simultaneously perform two searches – one from the starting point (forward search) and the other from the goal point (backward search). These searches progress in alternating steps until they meet, thereby creating a connecting path from the start to the goal.

By exploring the search space from both ends, it effectively narrows the exploration area, ultimately resulting in significant time and computational savings. This technique is specifically suitable for scenarios with well-defined and clearly connected start and goal states.

Implementing bidirectional search can lead to more efficient and optimized solutions in fields like transportation, robotics, network analysis, and other diverse applications where the shortest or most effective paths are crucial.

Examples of Bidirectional Search

Bidirectional Search is an algorithm used to find the shortest path between two nodes in a graph or a tree. It works by simultaneously searching from both the starting node and the target node until the two searches meet. This algorithm is highly efficient and is used in various real-world applications. Here are three examples:

GPS Navigation Systems:Bidirectional Search is widely used in GPS navigation systems to find the shortest path between the origin and destination points. The algorithm begins by searching outward from both the starting point and the destination, eventually meeting in the middle to form an optimal route. This significantly reduces search time and provides users with an accurate and efficient route to their destination.

Social Network Analysis:In the context of social networks, such as Facebook or LinkedIn, Bidirectional Search can be used to find the shortest distance (number of connections) between two individuals. By searching from both the source and target profiles simultaneously, the algorithm can quickly identify the optimal path between users, helping to uncover mutual connections, suggest potential friends/colleagues, or assist in network analysis studies.

Artificial Intelligence and Game Pathfinding:Bidirectional Search is used in artificial intelligence applications, particularly in pathfinding for computer games and robotics. For example, in a game with a large map, the algorithm can find the most efficient path for a character to move from one point to another, taking into account obstacles and terrain. In the case of robotics, the algorithm is employed to identify the most efficient plan for a robot to move from its current position to a target location, considering potential obstacles in its environment.


Bidirectional Search FAQ

1. What is bidirectional search?

Bidirectional search is an algorithm that searches simultaneously from both the source and goal nodes to find the shortest path in a graph or tree data structure. It uses two parallel searches: one from the source node (forward direction) and the other from the goal node (backward direction).

2. How does bidirectional search work?

Bidirectional search works by conducting two parallel searches – one from the source node, called forward search, and one from the goal node, called backward search. The algorithm explores the neighboring nodes of both search directions simultaneously, until they meet at a common node. The path from the source node to the goal node can then be constructed by combining the paths explored in both directions.

3. What are the advantages of bidirectional search?

Bidirectional search has several advantages over unidirectional search techniques, such as:

a. Reduced search time: Because the algorithm searches from both ends, it typically finds the shortest path more quickly than unidirectional search.

b. Improved efficiency: Bidirectional search can use fewer resources compared to unidirectional search, as it often requires fewer node expansions to reach the goal node.

4. In which scenarios is bidirectional search most effective?

Bidirectional search is most effective in scenarios where:

a. The search space is large and well-connected, which can make unidirectional search slow and resource-intensive.

b. Both the source and goal nodes are known, allowing for simultaneous exploration in both forward and backward directions.

c. The goal is to find the shortest path between two nodes, as bidirectional search is designed to quickly locate this path.

5. Can bidirectional search be used with other search algorithms?

Yes, bidirectional search can be combined with other search algorithms, such as Breadth-First Search (BFS), Depth-First Search (DFS), or A* search. Combining bidirectional search with these algorithms can lead to faster and more efficient searches, as it can leverage the benefits of both search techniques.


Related Technology Terms

  • Graph traversal algorithms
  • Breadth-First Search (BFS)
  • Depth-First Search (DFS)
  • Dijkstra’s Shortest Path Algorithm
  • Optimized Pathfinding

Sources for More Information


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