543_Diameter_of_Binary_Tree.java

class Solution {
    // 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);
        int R = depth(node.right);
        ans = Math.max(ans, L+R+1);
        return Math.max(L, R) + 1;
    }
}