LeetCode-in-Java

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

Medium

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

public class Solution {
    public int numSteps(String s) {
        int steps = 0;
        int carry = 0;
        for (int i = s.length() - 1; i >= 1; i--) {
            if (carry == 0) {
                if (s.charAt(i) == '1') {
                    steps += 2;
                    carry = 1;
                } else {
                    steps++;
                }
            } else {
                if (s.charAt(i) == '0') {
                    steps += 2;
                } else {
                    steps++;
                }
            }
        }
        return steps + carry;
    }
}

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