How Do You Find the Diameter of a Tree in Data Structure?


Angela Bailey

In the field of data structure, finding the diameter of a tree is a common problem. The diameter of a tree is defined as the longest path between any two nodes in the tree. It can be seen as the maximum distance that needs to be traveled to reach one node from another within the tree.

Understanding Trees in Data Structure

Trees are hierarchical data structures consisting of nodes connected by edges. Each node can have zero or more child nodes, except for the root node which has no parent. The topmost node in a tree is called the root, and every other node is called an internal node or leaf depending on whether it has children or not.

Finding the Diameter of a Tree

There are several algorithms to find the diameter of a tree, but one commonly used approach is through depth-first search (DFS). DFS explores each branch of a tree as deeply as possible before backtracking.

To find the diameter using DFS, we need to perform two depth-first searches:

  • Step 1: Pick an arbitrary node as the starting point and perform DFS to find the farthest node from it.
  • Step 2: Take that farthest node as the new starting point and perform another DFS to find the farthest node from it. The distance between these two farthest nodes will be the diameter of the tree.

The pseudocode for finding the diameter using DFS would look something like this:

function findDiameter(node):
    visited[node] = true
    maxDistance = 0
    farthestNode = node

    for each child in children[node]:
        if visited[child] == false:
            distance = findDiameter(child) + edgeWeight(node, child)
            if distance > maxDistance:
                maxDistance = distance
                farthestNode = child

    return maxDistance, farthestNode

startNode = any arbitrary node
distance1, farthest1 = findDiameter(startNode)
distance2, farthest2 = findDiameter(farthest1)

diameter = distance2


Let’s consider a simple tree with 5 nodes:

      /   \
     B     C
          / \
         D   E

If we start the DFS from node A, the farthest node will be E. Then if we start another DFS from E, the farthest node will be D. The distance between D and E will be the diameter of this tree.


Finding the diameter of a tree in data structure is an important problem to solve. It can be achieved using depth-first search to explore the tree and find the longest path between any two nodes. By following the steps outlined in this article, you can confidently find the diameter of any given tree.

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