Given a Number - N, count the number of set bits in N [This solution unsets the Least Significant Set Bit of the given N].

setbits2.cpp

// for previous solution: https://gist.github.com/Ch-sriram/212f8185414fcb71278c6028128fcb2a

// Intuition behind the solution:
// When we apply bitwise-AND the number N with N-1, we get a new number whose Least Significant Set Bit is Unset. 

int countSetBits (long long N) {
  int cnt = 0;
  while (N != 0) {
    ++cnt;
    N = N & (N-1);  // This is the unsetting step.
  }
  return cnt;
}