_543.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.TreeNode;

/**
 * Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

 Example:
 Given a binary tree
     1
    / \
   2   3
  / \
 4   5
 Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

 Note: The length of path between two nodes is represented by the number of edges between them.
 */
public class _543 {

    int diameter = 0;
    public int diameterOfBinaryTree(TreeNode root) {
        dfs(root);
        return diameter;
    }

    private int dfs(TreeNode root) {
        if (root == null) return 0;
        int left = dfs(root.left);
        int right = dfs(root.right);
        diameter = Math.max(diameter, left + right);
        return Math.max(left, right) + 1;
    }

}