543. Diameter of Binary Tree

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.

pre order traverse

int result = 0;
public int diameterOfBinaryTree(TreeNode root) {
    if(root == null) return 0;
    traverse(root);
    return result-1;
}

public int traverse(TreeNode root) {
    if(root == null) return 0;
    int left = traverse(root.left);
    int right = traverse(root.right);
    result = Math.max(result, 1+right+left);
    return Math.max(left, right) + 1;
}