Distribute Coins in Binary Tree.java

// Runtime: 1 ms (Top 58.67%) | Memory: 43.1 MB (Top 15.04%)
class Solution {
    int count = 0;
        public int helper(TreeNode root)
        {
            if(root == null)
                return 0;
            int left = helper(root.left);
            int right = helper(root.right);
            count+= Math.abs(left)+Math.abs(right);
            return (left+right+root.val-1);
        }
        public int distributeCoins(TreeNode root) {
            helper(root);
            return count;
        }
}