1404. Number of Steps to Reduce a Number in Binary Representation to One

Given a number s in their binary representation. Return the number of steps to reduce it to 1 under the following rules:

• If the current number is even, you have to divide it by 2.

• If the current number is odd, you have to add 1 to it.

It's guaranteed that you can always reach to one for all testcases.

 

Example 1:

Input: s = "1101"
Output: 6
Explanation: "1101" corressponds to number 13 in their decimal representation.
Step 1) 13 is odd, add 1 and obtain 14. 
Step 2) 14 is even, divide by 2 and obtain 7.
Step 3) 7 is odd, add 1 and obtain 8.
Step 4) 8 is even, divide by 2 and obtain 4.  
Step 5) 4 is even, divide by 2 and obtain 2. 
Step 6) 2 is even, divide by 2 and obtain 1.  

Example 2:

Input: s = "10"
Output: 1
Explanation: "10" corressponds to number 2 in their decimal representation.
Step 1) 2 is even, divide by 2 and obtain 1.  

Example 3:

Input: s = "1"
Output: 0

 

Constraints:

• 1 <= s.length <= 500
• s consists of characters '0' or '1'
• s[0] == '1'

思路：模擬這個過程來做就好了

class Solution(object):
    def numSteps(self, s):
        """
        :type s: str
        :rtype: int
        """
        res = 0
        cs = [int(c) for c in s][::-1]
        jinwei = 0
        for c in cs[:-1]:
            if jinwei == 0:
                if c == 1:
                    jinwei = 1
                    res += 2
                else:
                    res += 1
            else:
                if c == 1:
                    res += 1
                else:
                    res += 2
        if jinwei == 1:
            res += 1
        return res

s=Solution()
print(s.numSteps('1101'))
print(s.numSteps('10'))
print(s.numSteps('0'))