979

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int ans=0;
    int dfs(TreeNode* curr){
        if(!curr) return 0;
        int L = dfs(curr->left);
        int R = dfs(curr->right);
        ans += abs(L)+abs(R);
        return L+R+curr->val-1;
    }

    int distributeCoins(TreeNode* root) {
        dfs(root);
        return ans;
    }
};