GoLang: Reverse the Bits

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.

Follow up:
If this function is called many times, how would you optimize it?

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

Reverse the Bits using GoLang

We can go through each index and bit-or the corresponding index (at reversed location).

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func reverseBits(num uint32) uint32 {
    var ret = uint32(0)
    var power = uint32(31)
    for num != 0 {
        ret += (num & 1) << power
        num = num >> 1
        power -= 1
    }
    return ret
}

func reverseBits(num uint32) uint32 {
    var ret = uint32(0)
    var power = uint32(31)
    for num != 0 {
        ret += (num & 1) << power
        num = num >> 1
        power -= 1
    }
    return ret
}

Time and space complexity is O(1) – we are iterating 32 times and only use two variables (constant)

Reverse Bits of 32-bit Integer:

• Teaching Kids Programming – Reverse Bits of a 32-bit Integer
• How to Reverse Bits for 32-bit Unsigned Integer in C/C++?
• GoLang: Reverse the Bits

–EOF (The Ultimate Computing & Technology Blog) —