7. Reverse Integer

Runtime: 32 ms
class Solution(object):
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        rev=0
        if x<0:
            m=-1
        else:
            m=1
        i=x*m
        while i!=0:
            rev=rev*10+i%10
            i=i/10
            if rev>2**31:
                return 0
        else:
            return rev*m

Runtime: 68 ms
class Solution(object):
    def reverse(self, x):
        """
        :type x: int
        :rtype: int
        """
        if x<0:
            m=-1
        else:
            m=1

        s=str(m*x)
        rev=''
        for i in range(len(s)):
            rev+=s[-(i+1)]

        res=int(rev)
        if res <2**31:
            return res*m
        else:
            return 0