What Is Warshall Algorithm in Data Structure?


Angela Bailey

The Warshall algorithm, also known as the Floyd-Warshall algorithm, is a dynamic programming algorithm used to find the shortest path between all pairs of vertices in a weighted directed graph. It is named after its inventors, Robert Floyd and Stephen Warshall. The algorithm is widely used in various applications such as network routing, traffic optimization, and data mining.

Understanding the Problem

Before diving into the details of the Warshall algorithm, let’s first understand the problem it aims to solve. Given a weighted directed graph with n vertices and edges connecting them, our goal is to find the shortest path between every pair of vertices.

The Algorithm

The Warshall algorithm solves this problem by maintaining a matrix of distances between all pairs of vertices. The matrix is initially filled with the weights of the edges connecting each pair of vertices. Let’s call this matrix D (short for distance).

To find the shortest path between all pairs of vertices, we iterate over each vertex in the graph and update the distance matrix D. This process involves considering each vertex as an intermediate point between any two other vertices.

Iterative Process

The algorithm iterates over each vertex k from 1 to n and checks if there exists a shorter path from vertex i to vertex j through vertex k. If such a path exists, it updates the distance matrix accordingly.

This process can be summarized in three steps:

  • Step 1: Initialize the distance matrix with edge weights.
  • Step 2: Iterate over each vertex as an intermediate point (k).
  • Step 3: Update the distance matrix if a shorter path is found through vertex k.


The pseudocode for the Warshall algorithm can be written as follows:

for each vertex k
    for each vertex i
        for each vertex j
            D[i][j] = min(D[i][j], D[i][k] + D[k][j])

This triple nested loop ensures that all possible paths between any two vertices are considered and updated if a shorter path is found.

Time Complexity

The time complexity of the Warshall algorithm is O(n^3), where n is the number of vertices in the graph. This is because we need to iterate over each vertex as an intermediate point for every pair of vertices.


The Warshall algorithm is a powerful tool for finding the shortest path between all pairs of vertices in a weighted directed graph. Its application extends beyond just graphs and can be used in various optimization problems. By understanding and implementing this algorithm, you will have a valuable tool to tackle complex network optimization challenges.

Now that you have learned about the Warshall algorithm, you can apply it to solve real-world problems in various domains!

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