543. 二叉树的直径【简单】

https://leetcode-cn.com/problems/diameter-of-binary-tree/

class Solution {
    int maxDiameter = 0;

    public int diameterOfBinaryTree(TreeNode root) {
        maxDepth(root);
        return maxDiameter;
    }

    int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftMax = maxDepth(root.left);
        int rightMax = maxDepth(root.right);
        // 后序遍历位置顺便计算最大直径
        maxDiameter = Math.max(maxDiameter, leftMax + rightMax);
        return 1 + Math.max(leftMax, rightMax);
    }
}