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Swap Adjacent Bits

Description

Implement the missing code, denoted by ellipses. You may not modify the pre-existing code.

You’re given an arbitrary 32-bit integer n. Take its binary representation, split bits into it in pairs (bit number 0 and 1, bit number 2 and 3, etc.) and swap bits in each pair. Then return the result as a decimal number.

Example

  • For n = 13, the output should be swapAdjacentBits(n) = 14.

1310 = 11012 ~> {11}{01}2 ~> 11102 = 1410.

  • For n = 74, the output should be swapAdjacentBits(n) = 133.

7410 = 010010102 ~> {01}{00}{10}{10}2 ~> 100001012 = 13310.

Note the preceding zero written in front of the initial number: since both numbers are 32-bit integers, they have 32 bits in their binary representation. The preceding zeros in other cases don’t matter, so they are omitted. Here, however, it does make a difference.

Input/Output

  • [execution time limit] 4 seconds (js)

  • [input] integer n

    Guaranteed constraints:
    0 \leq n \le 2^{30}.

  • [output] integer

[JavaScript (ES6)] Syntax Tips

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// Prints help message to the console
// Returns a string
function helloWorld(name) {
console.log("This prints to the console when you Run Tests");
return "Hello, " + name;
}

Solution

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function swapAdjacentBits(n) {
  return parseInt(
    ((n.toString(2).length % 2 ? "0" : "") + n.toString(2))
      .match(/\d{2}/g)
      .map(el =>
        el
          .split("")
          .reverse()
          .join("")
      )
      .join(""),
    2
  );
}