Question

05.07. Exchange

中文文档

Description

Write a program to swap odd and even bits in an integer with as few instructions as possible (e.g., bit 0 and bit 1 are swapped, bit 2 and bit 3 are swapped, and so on).

Example1:

 Input: num = 2（0b10）

 Output 1 (0b01)

Example2:

 Input: num = 3

 Output: 3

Note:

1. 0 <= num <= 2^30 - 1
2. The result integer fits into 32-bit integer.

Solutions

Solution 1

class Solution:
  def exchangeBits(self, num: int) -> int:
    return ((num & 0x55555555) << 1) | ((num & 0xAAAAAAAA) >> 1)

class Solution {
  public int exchangeBits(int num) {
    return ((num & 0x55555555) << 1) | ((num & 0xaaaaaaaa)) >> 1;
  }
}

class Solution {
public:
  int exchangeBits(int num) {
    return ((num & 0x55555555) << 1) | ((num & 0xaaaaaaaa)) >> 1;
  }
};

func exchangeBits(num int) int {
  return ((num & 0x55555555) << 1) | (num&0xaaaaaaaa)>>1
}

impl Solution {
  pub fn exchange_bits(mut num: i32) -> i32 {
    let mut res = 0;
    let mut i = 0;
    while num != 0 {
      let a = num & 1;
      num >>= 1;
      let b = num & 1;
      num >>= 1;
      res |= a << (i + 1);
      res |= b << i;
      i += 2;
    }
    res
  }
}