868. Binary Gap

Input: 5
Output: 2
Explanation:
5 in binary is 0b101.

    def binaryGap(self, N):
        """
        :type N: int
        :rtype: int
        """
        s = bin(N)
        num = 0
        res = 0
        
        for i in s:
            if i == '1':
                if res != 0:
                    num = max(res,num)
                    res = 1
                else:
                    res += 1
            
            elif res !=0:
                res += 1

        return num

当然也可以用位运算去比较，通过从后到前的每一位数对比1，然后直接相减。更巧妙：

    def binaryGap(self, N):
        A = [i for i in xrange(32) if (N >> i) & 1]
        if len(A) < 2: return 0
        return max(A[i+1] - A[i] for i in xrange(len(A) - 1))