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 longestpath 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].

题目含义：求二叉树的直径，并告诉了我们直径就是两点之间的最远距离。这条直径可以不包含根节点

    private int maxLength = 0;
    private int maxDepth(TreeNode root)
    {
        if (root == null)return 0;
        int leftMaxDepth = maxDepth(root.left);
        int rightMaxDepth = maxDepth(root.right);
        maxLength = Math.max(maxLength,leftMaxDepth+rightMaxDepth);
        return Math.max(leftMaxDepth,rightMaxDepth)+1;
    }    
    public int diameterOfBinaryTree(TreeNode root) {
        maxDepth(root);
        return maxLength;
    }