Subtree with Maximum Average

题目描述：

Given a binary tree, find the subtree with maximum average. Return the root of the subtree.

样例：

     1
   /   \
 -5     11
 / \   /  \
1   2 4    -2 
return the node 11.

代码实现：

/**
 * 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 class ResultType {
        int sum;
        int size;
        TreeNode root;
        public ResultType(int sum, int size) {
            this.sum = sum;
            this.size = size;
        }
    }
    TreeNode maxtree = null;
    ResultType result = null;
    public TreeNode findSubtree2(TreeNode root) {
        helper(root);
        return maxtree;    
    }
    private ResultType helper(TreeNode root) {
        if (root == null) {
            return new ResultType(0, 0);
        }
        
        ResultType left = helper(root.left);
        ResultType right = helper(root.right);
        ResultType subresult = new ResultType(left.sum + right.sum + root.val,
                                              left.size + right.size + 1);
        
        if (maxtree == null || subresult.sum * result.size > subresult.size * result.sum) {
            maxtree = root;
            result = subresult; 
        }
        return subresult;
    }
}