面试题 05.03. 翻转数位

给定一个32位整数 num，你可以将一个数位从0变为1。请编写一个程序，找出你能够获得的最长的一串1的长度。

示例 1：

输入: num = 1775(110111011112)
输出: 8

示例 2：

输入: num = 7(01112)
输出: 4

Python 解答：
1.耿直的方法

class Solution:
    def reverseBits(self, num: int) -> int:
        def transform(n):
            n = ((1<<32)-1)&n
            res = [0 for i in range(32)]
            i = 0
            while n > 0:
                r = n&1
                res[i] = r
                n >>= 1
                i += 1
            return res
        res = transform(num)
        if sum(res) == 32:
            return 32
        max_value = 0
        for i in range(len(res)):
            if res[i] == 0:
                temp = res[::]
                temp[i] = 1
                count = 0
                for item in temp:
                    if item == 1:
                        count += 1
                        if count > max_value:
                            max_value = count 
                    else:
                        count = 0
        return max_value

2.单次遍历

class Solution:
    def reverseBits(self, num: int) -> int:
        n = ((1<<32)-1)&num
        pre = 0 
        cur = 0
        max_value = 1
        while n > 0:
            r = n&1
            if r:
                cur += 1
            else:
                if cur+pre+1 > max_value:
                    max_value = cur+pre+1
                pre = cur
                cur = 0
            n >>= 1
        else:
            max_value = max(max_value, cur+1+pre)
        return min(max_value, 32)