Today I have done leetcode's May LeetCoding Challenge with cpp.

May LeetCoding Challenge 29

Description

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

Given the binary representation of an integer as a string s, 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 is guaranteed that you can always reach one for all test cases.

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'

Solution

class Solution {
public:
  int numSteps(string s) {
    reverse(s.begin(), s.end());
    int carry = 0;
    int answer = 0;
    int ones = 0;
    for(auto c : s) {
      if((carry && c == '0') || (!carry && c == '1')) {
        answer += 2;
      } else {
        answer += 1;
      }
      ones += (c == '1');
      if(ones) carry = 1;
    }
    return answer - (ones == 1) * 2;
  }
};