563. Binary Tree Tilt

• Difficulty: Easy

• Topics: Tree

• Similar Questions:

Problem:

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:

Solutions:

/**
 * 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 findTilt(TreeNode* root) {
        int tilt = 0;
        helper(root, tilt);
        return tilt;
    }

private:
    int helper(TreeNode* root, int& tilt) {
        if (root == nullptr) {
            return 0;
        }

        int left = helper(root->left, tilt);
        int right = helper(root->right, tilt);

        tilt += abs(left - right);
        return root->val + left + right;
    }

};