Subtree with Maximum Average

我写的

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root the root of binary tree
     * @return the root of the maximum average of subtree
     */
    private TreeNode node;
    private double maxAverage = Double.MIN_VALUE;
    
    public TreeNode findSubtree2(TreeNode root) {
        // Write your code here
        
        helper(root);
        return node;
        
    }
    private double helper(TreeNode root) {
        if (root == null) {
            return 0;
        }
        //改成double
        double left = helper(root.left);
        double right = helper(root.right);
        double sum = root.val + left + right;
        int n = count(root);
        if (sum / n > maxAverage) {
            maxAverage = sum / n;
            node = root;
        }
        return sum;
    }
    private int count(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftcount = count(root.left);
        int rightcount = count(root.right);
        return leftcount + rightcount + 1;
    }
}