Pow(x,n).md

50. Pow(x, n)

Implement pow(x, n).

Example 1:

Input: 2.00000, 10
Output: 1024.00000

Example 2:

Input: 2.10000, 3
Output: 9.26100

Method:

n-=1 in each turn, tle:

class Solution(object):
    def myPow(self, x, n):
        """
        :type x: float
        :type n: int
        :rtype: float
        """
        if n==0:
            return 1
        if n<0:
            x=1.0/x
            n=-n
        t=x
        while n-1:
            x*=t
            n-=1
        return x

Solution:

n/2 in each turn:

recursion:

class Solution(object):
    def myPow(self, x, n):
        """
        :type x: float
        :type n: int
        :rtype: float
        """
        if n==0:
            return 1
        if n<0:
            x=1.0/x
            n=-n
        if n%2:
            return x*self.myPow(x*x, n/2)
        return self.myPow(x*x, n/2)

iteration:

class Solution(object):
    def myPow(self, x, n):
        """
        :type x: float
        :type n: int
        :rtype: float
        """
        if n==0:
            return 1
        if n<0:
            x=1.0/x
            n=-n
        res=1
        while n:
            if n%2:
                res*=x
            x*=x
            n/=2
        return res