563. Binary Tree Tilt.cpp

/**
 * 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) {
        if(root == NULL) return 0;
        
        int res = 0;
        
        postorder(root, res);
        
        return res;
    }
private:
    int postorder(TreeNode* root, int& res){
        if(root == NULL) return 0;
        
        int leftsum= postorder(root->left,res);
        
        int rightsum = postorder(root->right,res);
        
        res += abs(leftsum - rightsum);
        
        return leftsum + rightsum + root->val;
        
    }
};