9-基础练习 十进制转十六进制

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		String[] two = {
				"0", "1", "2", "3",
				"4", "5", "6", "7",
				"8", "9", "A", "B",
				"C", "D", "E", "F",
				}; 	
		Scanner cin = new Scanner(System.in);
		long a = cin.nextLong();
		StringBuilder toTwo = new StringBuilder();
		if(a == 0) {
			System.out.println("0");
			return ;
		}
		while(a != 0) {
			toTwo.append(a % 2 + "");
			a = a / 2;
		}
		int len = toTwo.length();
//		String toTwo2 = toTwo.toString();
		if(len % 4 == 1) {
			toTwo.append("000");
		}
		else if(len % 4 == 2) {
			toTwo.append("00");
		}
		else if(len % 4 == 3) {
			toTwo.append("0");
		}
		len = toTwo.length();
		StringBuilder ans = new StringBuilder();
		for(int i = 0; i < len - 3; i += 4) {
			int t = (toTwo.charAt(i) - ‘0‘) * 1 + (toTwo.charAt(i+1) - ‘0‘) * 2 +
					(toTwo.charAt(i+2) - ‘0‘) * 4 + (toTwo.charAt(i+3) - ‘0‘) * 8;
			ans.append(two[t]);
		}
		System.out.println(ans.reverse());
	}
}