华为机试测试- 大数相加

方法一：

直接使用BigDecimal

方法二：字符串解析，注意stringBuilder.append(int x)这里的x最终会变成x字符串,而不是对应的char.

　　比较好的算法

import java.math.BigDecimal;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        String t1=scanner.next();
        String t2=scanner.next();
        System.out.println(getStr(t1, t2));
        scanner.close();
    }
    
    public static String getStr(String a,String b)
    {
        int l=a.length();
        int s=b.length();
        String longString=l>s?a:b;
        String shortString=l<=s?a:b;
        l=longString.length();
        s=shortString.length();
        longString=new StringBuilder(longString).reverse().toString();
        shortString=new StringBuilder(shortString).reverse().toString();
        StringBuilder stringBuilder=new StringBuilder();
        boolean carry=false;
        for(int i=0;i<s;i++)
        {
            char cl=longString.charAt(i);
            char cs=shortString.charAt(i);
            int il=cl-'0';
            int is=cs-'0';
            int nx=il+is+(carry?1:0);
            if(nx>9)
            {
                carry=true;
                stringBuilder.append((char)('0'+nx-10));
            }
            else {
                carry=false;
                stringBuilder.append((char)('0'+nx));
            }
        }
        if(s==l && carry)
        {
            stringBuilder.append('1');
            return stringBuilder.toString();
        }
        String str=longString.substring(s,l);
        for(int i=0;i<str.length();i++)
        {
            char c=str.charAt(i);
            int nx=c-'0'+(carry?1:0);
            if(nx>9)
            {
                carry=true;
                stringBuilder.append((char)('0'+nx-10));
            }
            else {
                carry=false;
                stringBuilder.append((char)('0'+nx));
            }
        }
        if(carry)
            stringBuilder.append('1');
        return stringBuilder.reverse().toString();
    }
}