Binary to Decimal

/*
 * Problem : Convert a binary number to decimal.
 * Input   : One text made of the digits 0 and 1.
 * Output  : The decimal value.
 * Approach: Read the bits from left to right: result = result * 2 + bit.
 * Time    : O(d)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        String bits = new Scanner(System.in).next();

        // Step 1: The result starts at 0.
        long result = 0;

        // Step 2: Read the bits from left to right.
        for (int index = 0; index < bits.length(); index++) {
            // Step 3: Turn the character into a number. The character '1' minus the character '0' is the number 1.
            int bit = bits.charAt(index) - '0';

            // Step 4: Multiply the result by 2 and add the bit. Example: 10 -> 10 * 2 + 1 = 101.
            result = result * 2 + bit;
        }

        // Step 5: Print the decimal value.
        System.out.println(result);
    }
}