190. Reverse Bits

Problem

Tags: Divide and Conquer, Bit Manipulation

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?

Code

JS

// 190. Reverse Bits (6/16/53748)
// Runtime: 128 ms (3.59%) Memory: 40.50 MB (93.50%) 

/**
 * @param {number} n - a positive integer
 * @return {number} - a positive integer
 */
function reverseBits(n) {
    let result = 0;
    for (let i = 0; i < 32; i++) {
        result = (result << 1) + (n & 1);
        n >>= 1;
    }
    return result >>> 0;
}