二叉树求深度模板

543. 二叉树的直径

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int res;
    public int diameterOfBinaryTree(TreeNode root) {
            dfs(root);
        return res;
    }
    public int dfs(TreeNode root){
        if(root == null) return 0;
        
        int LD = dfs(root.left);
        int RD = dfs(root.right);
        
        res = Math.max(res,LD+RD);
        return 1+Math.max(LD,RD);
        
    }
    
}