PAT乙级 1048 数字加密 (20 分) Java 实现

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本文提供PAT1048题目的两种解决方案，重点介绍了如何处理字符串加密问题，包括位数差计算、数字相加及减法运算，并通过13取余实现加密。文章对比了两种解题思路，帮助读者理解最优解。

笔者首先是这么写的，但是只有3分

import java.util.Scanner;

public class pat1048 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
		String A = input.next();
		String B = input.next();
		String output = "";
		int diff = B.length() - A.length();		//计算两个数字的位数差；
		if(diff<0) diff = 0;					//如果A的长度大于B的长度，diff归零
		for(int i=0;i<diff;i++) output += (B.charAt(i)-'0'); 			//先输出不加密部分
		
		String[] arr = {"0","1","2","3","4","5","6","7","8","9","J","Q","K"};
		for(int i=diff;i<B.length();i++) {
			if(i%2==0) {				//如果是奇数，因为第一位diff是0，所以奇偶是反的
				int num = (B.charAt(i) - '0') + (A.charAt(i-diff) - '0');	//两数相加
				num = num%13;			//13取余
				output += arr[num];
			}else {
				int num = (B.charAt(i) - '0') - (A.charAt(i-diff) - '0');	//B-A
				if(num<0) num += 10;	//负数加10
				output += arr[num];
			}
		}
		System.out.println(output);
	}

}

这是通过学习PauperGuy代码，改过以后的代码，我愿称这道题目的判定为NT，什么都没多学到，浪费了半小时。

import java.util.Scanner;

public class pat1048 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
		String A = input.next();
		String B = input.next();
		String output = "";
		String[] arr = {"0","1","2","3","4","5","6","7","8","9","J","Q","K"};
		int len;
		int diff = A.length() - B.length();		//计算两个数字的位数差；
		if(diff<0) for(int i=0;i<Math.abs(diff);i++) A = "0" + A;		//如果B比A长，就用 “0” 来补全A
		else for(int i=0;i<diff;i++) B = "0" + B;						//A比B长，补全B
		
		char[] arrA = A.toCharArray(), arrB = B.toCharArray();
		len = arrA.length;
		for(int i=len-1;i>=0;i--) {
			if((len-i)%2==1) {				//如果是奇数，因为第一位diff是0，所以奇偶是反的
				int num = (arrB[i] - '0') + (arrA[i] - '0');	//两数相加
				num = num%13;			//13取余
				output = arr[num] + output;
			}else {
				int num = (arrB[i] - '0') - (arrA[i] - '0');	//B-A
				if(num<0) num += 10;	//负数加10
				output = arr[num] + output;
			}
		}
		System.out.println(output);
	}

}