543. Diameter of Binary Tree

Question:

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.

Solution:

  • Method 1: Divide and conquer(Recursion). ```Java /**
    • Definition for a binary tree node.
    • public class TreeNode {
    • int val;
    • TreeNode left;
    • TreeNode right;
    • TreeNode(int x) { val = x; }
    • } */ class Solution { private int result; public int diameterOfBinaryTree(TreeNode root) { if(root == null) return 0; maxPath(root); return this.result - 1; } private int maxPath(TreeNode root){ if(root == null) return 0; int left = maxPath(root.left); int right = maxPath(root.right); this.result = Math.max(result, left + right + 1); return Math.max(left, right) + 1; } } ```