Algorithm learning personally note

Added some Sys Design leanring note

Power(x, n) x^n = (x^(n.2))^2 -> )(logn)

sqrt(x) magic number 0x5f3759df

Trailing Number of zeros in n! n/5 + n/25 + n/123

O(1) check power of 2 (x-1) & x == 0 --> x 是 2 的某次幂