543. Diameter of Binary Tree.md

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).

  /**
   * 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;
      }
  }