Leetcode 190. Reverse Bits

190. Reverse Bits

• Total Accepted: 71291
• Total Submissions: 242226
• Difficulty: Easy

Reverse bits of a given 32 bits unsigned integer.

For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00111001011110000010100101000000).

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

思路：二进制数反转。

代码：

方法一：

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        n = (n >> 16) | (n << 16);
        n = ((n & 0xff00ff00) >> 8) | ((n & 0x00ff00ff) << 8);
        n = ((n & 0xf0f0f0f0) >> 4) | ((n & 0x0f0f0f0f) << 4);
        n = ((n & 0xcccccccc) >> 2) | ((n & 0x33333333) << 2);
        n = ((n & 0xaaaaaaaa) >> 1) | ((n & 0x55555555) << 1);
        return n;
    }
};

 

方法二：

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