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public class Solution {
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  // you need treat n as an unsigned value
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  public int reverseBits(int n) {
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    int mask = 0;
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    int smask = 0;
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    int j = 0;
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    int rev = 0;
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    // basically we are checking that the number is set bit or not
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    // if the number is set bit then we are appending that to our main answer i.e, rev
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    for (int i = 31; i >= 0; i--) {
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      mask = 1 << i;
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      if ((mask & n) != 0) {
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        smask = 1 << j;
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        rev = rev | smask;
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      }
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      j++;
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    }
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    // Time Complexity : O(32 for int)
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    // Space Complexity : O(1)
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    return rev;
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  }
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}