190. Reverse Bits

Easy
Reverse bits of a given 32 bits unsigned integer.
Note:
  • Note that in some languages, such as Java, there is no unsigned integer type. In this case, both input and output will be given as a signed integer type. They should not affect your implementation, as the integer's internal binary representation is the same, whether it is signed or unsigned.
  • In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 2 above, the input represents the signed integer -3 and the output represents the signed integer -1073741825.
Example 1:
Input: n = 00000010100101000001111010011100
Output:
964176192 (00111001011110000010100101000000)
Explanation:
The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596, so return 964176192 which its binary representation is 00111001011110000010100101000000.
Example 2:
Input: n = 11111111111111111111111111111101
Output:
3221225471 (10111111111111111111111111111111)
Explanation:
The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is 10111111111111111111111111111111.
Constraints:
  • The input must be a binary string of length 32
Follow up: If this function is called many times, how would you optimize it?
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解題

第一種解法是使用 Go bits package 內的函式。
func reverseBits(num uint32) uint32 {
return bits.Reverse32(num)
}
第二種是透過shift把位元移到reverse後的位置。
func reverseBits(num uint32) uint32 {
var result uint32
for i := 0; i < 32; i++ {
result += num >> i << 31 >> i
}
return result
}