leetcode-190-Reverse Bits

leetcode-190-Reverse Bits

 

Reverse Bits

 

Reverse bits of a given 32 bits unsigned integer.

For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as00111001011110000010100101000000).

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

 

 

將一個數的二進制反過來，求反過來的數。
期，將該數的最低位，作為最高位即可（2^31）,然後依次求解。
例： 對於 0000..........10 ans = 0 ans += 0*(2^31) ans += 1*(2^30) ... ...

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        uint32_t i = 1 ,ans = 0,m = 31; // 要用uint32_t 不能用int  
        while (m --) { //  將 i = 2^31
            i <<= 1;
        }
        
        m = 32;
        while (n) {  // m --     用m-- 和n 都可以   
            ans += (n&1)*i;
            i >>= 1;
            n >>= 1;
        }
        return ans;
    }
};