https://leetcode-cn.com/problems/shu-zhi-de-zheng-shu-ci-fang-lcof/
func myPow(x float64, n int) float64 { var R func(x float64, m int) float64 R = func(x float64, m int) float64 { if m == 0 { return 1 } n := m % 2 h := R(x, m/2) if n == 0 { return h * h } else { return h * h * x } } if n >= 0 { return R(x, n) } else { return 1 / R(x, -n) } }