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/**
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 * Definition for a binary tree node.
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 * function TreeNode(val, left, right) {
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 *     this.val = (val===undefined ? 0 : val)
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 *     this.left = (left===undefined ? null : left)
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 *     this.right = (right===undefined ? null : right)
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 * }
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 */
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/**
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 * @param {TreeNode} root
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 * @return {boolean}
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 */
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var isBalanced = function (root) {
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    if (!root) {
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        return true;
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    }
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    return isBalanced(root.left) && isBalanced(root.right) && Math.abs(getSum(root.left) - getSum(root.right)) <= 1
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};
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function getSum(node) {
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    if (!node) {
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        return 0;
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    }
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    let dep = 1;
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    dep += Math.max(getSum(node.left), getSum(node.right));
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    return dep;
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}