[LintCode] 597 Subtree with Maximum Average 解題報告

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

Notice
LintCode will print the subtree which root is your return node.
It's guaranteed that there is only one subtree with maximum average.


Example
Given a binary tree:

     1
    /   \
 -5     11
 / \     /  \
1   2 4    -2

return the node 11.

5/8/2017

算法班

未經測試

public class Solution {
    /**
     * @param root the root of binary tree
     * @return the root of the maximum average of subtree
     */
    
    class Result {
        int sum;
        int size;
        TreeNode root;
        Result(TreeNode root, int sum, int size) {
            this.root = root;
            this.sum = sum;
            this.size = size;
        }
    }

    private Result subtree = null;

    public TreeNode findSubtree2(TreeNode root) {
        if (root == null) return null;
        Result _ = getMaxAverage(root);
        return subtree.root;
    }
    private Result getMaxAverage(TreeNode root) {
        if (root.left == null && root.right == null) {
            Result ret = new Result(root, root.val, 1);
            if (subtree == null || subtree.sum < root.val * subtree.size) {
                subtree = ret;
            }
            return ret;
        }
        Result left = root.left == null ? null: getMaxAverage(root.left);
        Result right = root.right == null ? null: getMaxAverage(root.right);
        Result current = new Result(root, root.val + left == null? 0: left.sum + right == null? 0: right.sum, 1 + left == null? 0: left.size + right == null? 0: right.size);
        if (subtree == null || current.sum * subtree.size > subtree.sum * current.size) {
            subtree = current;
        }
        return current;
    }
}

九章解法

https://www.jiuzhang.com/solutions/subtree-with-maximum-average/