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class Solution {
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  public boolean isPowerOfTwo(int n) {
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    return power2(0, n);
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  }
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  public boolean power2(int index, int n) {
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    if (Math.pow(2, index) == n) return true;
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    if (Math.pow(2, index) > n) return false;
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    return power2(index + 1, n);
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  }
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}