[LeetCode] 190. Reverse Bits - Java

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

Reverse Bits - LeetCode

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문제

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

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풀이

풀이 과정

주어진 32비트 정수를 거꾸로 구하는 문제이다.

정답 변수 answer를 0으로 초기화하고 n 비트를 순회하며 다음의 과정을 반복한다.

• answer를 왼쪽 shift
• n의 마지막 비트( n과 1의 AND 연산)를 answer에 마지막에 추가 ( OR연산 ) 
• n 오른쪽 shift

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최종 코드

public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        int answer = 0;

        for(int i = 0; i < 32; i++){
            // 정답 비트를 왼쪽으로 한칸 이동
            answer <<= 1;
            // 현재 n의 맨 마지막 비트를 정답의 마지막에 추가
            answer |= (n & 1);
            // n의 비트를 오른쪽으로 한 칸 이동
            n >>= 1;
        }

        return answer;
    }
}

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