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.
实现：
int max = 0; public int diameterOfBinaryTree(TreeNode root) { maxDepth(root); return max; } private int maxDepth(TreeNode root) { if (root == null) return 0; int left = maxDepth(root.left); int right = maxDepth(root.right); max = Math.max(max, left + right); return Math.max(left, right) + 1; }思路： 前序遍历二叉树，用max保存当前最大值并决定是否更新
