Distribute Coins in Binary Tree LeetCode solution in Java

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class Solution {
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  int count = 0;
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  public int helper(TreeNode root) {
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    if (root == null) return 0;
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    int left = helper(root.left);
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    int right = helper(root.right);
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    count += Math.abs(left) + Math.abs(right);
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    return (left + right + root.val - 1);
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  }
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  public int distributeCoins(TreeNode root) {
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    helper(root);
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    return count;
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  }
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}