문제를 푼 날: 2022년 11월 13일 오후 2:40 (GMT+9)

https://leetcode.com/problems/reverse-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.

Example 1:

Input: n = 00000010100101000001111010011100
Output:    964176192 (00111001011110000010100101000000)
Explanation:The input binary string00000010100101000001111010011100 represents the unsigned integer 43261596, so return 964176192 which its binary representation is00111001011110000010100101000000.

Example 2:

Input: n = 11111111111111111111111111111101
Output:   3221225471 (10111111111111111111111111111111)
Explanation:The input binary string11111111111111111111111111111101 represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is10111111111111111111111111111111.

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?

Solution

일단은 생각나는 대로 풀었는데, 왜 음수인 경우에는 1을 추가로 더해야 하는지는 잘 모르겠다.

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        uint32_t ret = 0;
        uint32_t isMinus = (n & (1<<31));
        
        for(int i=0;i<31;++i){
            ret |= (n & 1);
            ret <<= 1;
            n >>= 1;
        }
        
        if(isMinus) ++ret;
        
        return ret;
    }
};