Concatenation of Consecutive Binary Numbers LeetCode solution in Java

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class Solution {
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  public int concatenatedBinary(int n) {
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    long res = 0;
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    for (int i = 1; i <= n; i++) {
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      res = (res * (int) Math.pow(2, Integer.toBinaryString(i).length()) + i) % 1000000007;
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    }
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    return (int) res;
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  }
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}