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

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# 題目敘述

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

# 解題思路

# Solution

class Solution {

    public int numSteps(String s) {

        int steps = 0;

        int carry = 0;

        for (int i = s.length() - 1; i > 0; i--) {

            int num = s.charAt(i) - '0' + carry;

            carry = 1;

            if(num == 0)  carry = 0;

            else if(num == 1) steps++;

            steps++;

        }

        return (carry == 1) ? steps + 1 : steps;

    }

}