563. Binary Tree Tilt

最新推荐文章于 2017-09-14 21:04:48 发布

SHURamos

最新推荐文章于 2017-09-14 21:04:48 发布

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分类专栏： Leetcode

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本文介绍了一种计算二叉树整体倾斜的方法。倾斜定义为树中每个节点左右子树节点值之和的绝对差，而整个二叉树的倾斜则是所有节点倾斜值之和。通过递归辅助函数实现，该函数同时计算子树节点值总和及每个节点的倾斜。

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Given a binary tree, return the tilt of the whole tree.

The tilt of a tree node is defined as the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.

The tilt of the whole tree is defined as the sum of all nodes' tilt.

Example:

Input: 
         1
       /   \
      2     3
Output: 1
Explanation: 
Tilt of node 2 : 0
Tilt of node 3 : 0
Tilt of node 1 : |2-3| = 1
Tilt of binary tree : 0 + 0 + 1 = 1

Note:

The sum of node values in any subtree won't exceed the range of 32-bit integer.
All the tilt values won't exceed the range of 32-bit integer.

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private int sum = 0;
    public int findTilt(TreeNode root) {
        helper(root);
		return sum;
    }
    private int helper(TreeNode root) {
		if (root == null)
			return 0;
		int left = helper(root.left);
		int right = helper(root.right);
		sum += Math.abs(left - right);
		return root.val + left + right;
	}
}