50. Pow(x, n)

50. Pow(x, n)

快速幂

func myPow(x float64, n int) float64 {
    //从1 向后逐步延伸 
    if n < 0 {
        x = 1 / x
        n = -n
    }
    var pow float64
    pow = 1
    for n >= 1{
        if  n & 1 == 1 {
            pow *= x
        }
        n = n >> 1
        x *= x
    }
    return pow
}