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;
    }
}