leetcode 563. 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:

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.

深搜的时候记录左子树右子树的和，然后做差求和。

/**
 * 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 sum = 0;
    int dfs(TreeNode* root) {
        if (root == nullptr) return 0;
        if (root->left == nullptr && root->right == nullptr) return root->val;
        int sum1 = 0;
        int sum2 = 0;
        sum1 += dfs(root->left);
        sum2 += dfs(root->right);
        sum += abs(sum1 - sum2);
        return sum1+sum2+root->val;
    }
    int findTilt(TreeNode* root) {
        dfs(root);
        return sum;
    }
};