5/14-5/20 CareerCup 5.4

Explain what the following code does: ((n & (n - 1)) == 0)

https://github.com/writecoffee/c ... blob/master/5.4.cpp


////////////////////////////////////////////////////////////////////////////////////
// GIST
//         judge whether n has only one bit flipped on or not
//
// WHY IS THAT
// 1.        n-1 flips the least significant 1 bit (x) and all zero bit lower than that,
//        so excluding the higher bits (for those between bit (x+1) and 31), n&(n-1)
//        generates 0.
// 2.        after that, we can put sight on bit between (x+1) and 31, for which can
//        influence the final result
//       
// OBSERVATION
//         by observation, this expression can only apply to positive interger
//        and the smallest negative number (-2^31), which most significant bit
//        is set to 1; except that, all negtive number has at least 2 bits on
////////////////////////////////////////////////////////////////////////////////////

writecoffee1 发表于 2012-6-9 20:14
https://github.com/writecoffee/career_cup_iteration/blob/master/5.4.cpp

同上，经典题 了

判断n是不是只有一个bit为1，连续的用这种方法可以count n中1的个数