Method diameterOfBinaryTree

java/543_Diameter_of_Binary_Tree.java:4–8

(TreeNode root)

    // https://leetcode.com/problems/diameter-of-binary-tree/solution/
    int ans;
    public int diameterOfBinaryTree(TreeNode root) {
        ans = 1;
        depth(root);
        return ans - 1;
    }
    public int depth(TreeNode node) {
        if (node == null) return 0;
        int L = depth(node.left);