思路：
- 内心知道这种方法是可以通过的，但是贼鸡儿麻烦。
- 输入两个字符串。按照笔算乘法的方式，循环计算。考虑到进位的问题。
代码：
package top.simuhunluo;
import java.util.Scanner;
public class Main {
static StringBuffer[] results;
static boolean z = true;
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String a = scanner.next();
String b = scanner.next();
int a_len = a.length();
int b_len = b.length();
StringBuffer str_a = new StringBuffer(a);
StringBuffer str_b = new StringBuffer(b);
results = new StringBuffer[b_len];
for (int i = b_len - 1, k = 0; i >= 0; i--, k++) {
results[k] = new StringBuffer(a_len + b_len);
int digit_b = str_b.charAt(i) - '0';
int jinwei = 0;
int yushu = 0;
for (int j = a_len - 1; j >= 0; j--) {
int digit_a = str_a.charAt(j) - '0';
int temp = digit_a * digit_b + jinwei;
jinwei = temp / 10;
yushu = temp % 10;
results[k].append(yushu);
}
results[k].append(jinwei);
}
for (int i = 0; i < results.length; i++) {
for (int j = 0; j < i; j++) {
results[i].insert(0, '0');
}
for (int j = 0; j < results.length - 1 - i; j++) {
results[i].append('0');
}
}
System.out.println(add(results));
}
public static StringBuffer add(StringBuffer[] results) {
StringBuffer stringBuffer = new StringBuffer();
int nums = results.length;//加数的个数
int jinwei = 0;
for (int i = 0; i < results[0].length(); i++) {
int tmp = 0;
for (int j = 0; j < nums; j++) {
tmp = tmp + results[j].charAt(i) - '0';
}
tmp += jinwei;
jinwei = tmp / 10;
int yushu = tmp % 10;
stringBuffer.append(yushu);
}
stringBuffer.append(jinwei);
stringBuffer = stringBuffer.reverse();
while (stringBuffer.charAt(0) == '0') stringBuffer.deleteCharAt(0);
return stringBuffer;
}
}