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class Solution {
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  public int[] sortByBits(int[] arr) {
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    Integer[] arrInt = new Integer[arr.length];
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    for (int i = 0; i < arr.length; i++) {
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      arrInt[i] = arr[i];
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    }
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    Arrays.sort(
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        arrInt,
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        new Comparator<Integer>() {
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          @Override
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          public int compare(Integer a, Integer b) {
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            int aBits = numOfBits(a);
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            int bBits = numOfBits(b);
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            if (aBits == bBits) {
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              return a - b;
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            }
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            return aBits - bBits;
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          }
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        });
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    for (int i = 0; i < arr.length; i++) {
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      arr[i] = arrInt[i];
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    }
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    return arr;
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  }
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  public int numOfBits(int a) {
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    int bits = 0;
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    while (a != 0) {
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      bits += a & 1;
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      a = a >>> 1;
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    }
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    return bits;
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  }
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}