LeetCode-190. Reverse Bits [C++][Java]

LeetCode-190. Reverse Bitshttps://leetcode.com/problems/reverse-bits/

题目描述

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.

解题思路

【C++】

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        uint32_t ans = 0;
        for (int i = 0; i < 32; ++i) {
            ans <<= 1;
            ans += n & 1;
            n >>= 1;
        }
        return ans;
    }
};

或者

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        uint32_t r = 0;
        for (int i = 0; i < 32; ++i) {
            r = r << 1;
            r = r | (n & 1u);
            n = n >> 1;
        }
        return r;
    }
};

【Java】

public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        long ans = 0;
        for (int i = 0; i < 32; ++i) {
            ans <<= 1;
            ans += n & 1;
            n >>= 1;
        }
        return (int)ans;
    }
}