题目

public class Main {
	public static void main(String[] args) {
		String str = "2021ABCD";
		int k = 0;
		long sum = 0;
		for(int i=str.length()-1;i>=0;i--,k++) {
			char c = str.charAt(i);
			if(c>='A'&&c<='D') {
				int res = c-'A'+10;
				sum+=(long)res*Math.pow(16,k);
			}else {
				int res = c-'0';
				sum+=(long)res*Math.pow(16, k);
			}
		}
		System.out.println(sum);
	}
}

public class Main {
	public static void main(String[] args) {
		String str = "2021ABCD";
		int k = 0;
		int sum = 0;
		for(int i=str.length()-1;i>=0;i--,k++) {
			char c = str.charAt(i);
			if(c>='A'&&c<='D') {
				int res = c-'A'+10;
				sum+=res*Math.pow(16,k);
			}else {
				int res = c-'0';
				sum+=res*Math.pow(16, k);
			}
		}
		System.out.println(sum);
	}
}

public class Main {
	public static void main(String[] args) {
		String s = "2021ABCD";
		int sum = 0;
		int j = 0;
		for(int i=s.length()-1;i>=0;i--,j++) {
			char c = s.charAt(i);
			if(c>='A'&&c<='D') {
				int sc = c-'A'+10;
				sum += sc*Math.pow(16,j);
			}else {
				int sc = c-'0';
				sum += sc*Math.pow(16,j);
			}
		}
		System.out.println(sum);
	}
}