https://leetcode.com/problems/binary-tree-tilt/description/
挺好的一个题目，审题不清的话很容易做错。主要是tilt of whole tree 的定义是sum of all node's tilt 而不是想当然的tilt of root.
一开是我就以为是简单的tilt of root 导致完全错误。思路其实可以看作是求sum of children 的变种，只是这里不仅要跟踪每个子树的sum 还要累计上他们的tilt。
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int tiltIter(TreeNode* root, int *t) {
if (root == nullptr) {
return ;
} int leftSum = ;
int rightSum = ;
if (root->left != nullptr) {
leftSum = tiltIter(root->left, t);
}
if (root->right != nullptr) {
rightSum = tiltIter(root->right, t);
}
//tilt of the current node;
int tilt = abs(leftSum - rightSum);
*t += tilt;
return root->val + leftSum + rightSum;
} int findTilt(TreeNode* root) {
int tilt = ;
tiltIter(root, &tilt);
return tilt;
}
};