LeetCode Binary Tree Tilt 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:

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

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定义二叉树一个节点的tilt为其左子树元素之和与右子树元素之和的差的绝对值。整棵二叉树的tilt为所有节点的tilt之和。现在要求一棵二叉树的tilt。 简单题，递归求解元素之和，然后更新tilt。都是递归到叶子节点，然后累加和往父亲节点走。 代码如下： [cpp] class Solution { private: void dfs(TreeNode* root, int& sum, int& tilt){ if(root == NULL) { sum = 0; tilt = 0; } else { int lsum = 0, rsum = 0, ltilt = 0, rtilt = 0; dfs(root->left, lsum, ltilt); dfs(root->right, rsum, rtilt); sum = lsum + rsum + root->val; tilt = ltilt + rtilt + abs(lsum – rsum); } } public: int findTilt(TreeNode* root) { int sum = 0, tilt = 0; dfs(root, sum, tilt); return tilt; } }; [/cpp] 本代码提交AC，用时16MS。]]>