543. 二叉树的直径 --力扣 --JAVA

class Solution {
    private int ans;
    public int diameterOfBinaryTree(TreeNode root) {
        dfs(root);
        return ans;
    }
    public int dfs(TreeNode root){
        if(root == null) {
            return -1;
        }
        int leftLength = dfs(root.left) + 1;
        int rightLength = dfs(root.right) + 1;
        ans = Math.max(ans, leftLength + rightLength);
        return Math.max(leftLength, rightLength);
    }
}