一 题目

• Input:
  • String a = "15324564...1455445"; //数字过长，不能转换为int/long型运算
  • String b = "45645612...145"; //数字过长，不能转换为int/long型运算
• Output:
  • x = a + b
• 基本思路：
  • 分别转换为字符数组
  • 从后向前(右对齐)，逐位运算

源码实现

import java.util.Scanner;

public class BigDecimalAdd {
    public static String convertIntArrayToString(int[] intArray) {
        StringBuffer stringBuffer = new StringBuffer();
        boolean isNotStart = true; //从左至右， 只要一直遇到的是0，则为true
        for (int i = 0; i < intArray.length; i++) {
            if (isNotStart) {
                if (intArray[i] != 0) {
                    isNotStart = false;
                    stringBuffer.append(intArray[i]);
                }
            } else {
                stringBuffer.append(intArray[i]);
            }
        }
        return stringBuffer.toString();
    }

    public static String plus(String a, String b) { //大数相加
        char[] numbersA = a.toCharArray();
        char[] numbersB = b.toCharArray();
        int maxLength = numbersA.length > numbersA.length ? numbersA.length : numbersB.length;
        int minLength = numbersA.length < numbersA.length ? numbersA.length : numbersB.length;
        int[] result = new int[maxLength + 1];//默认 各位初始化值为0
        int bitOperateResult; //保存位运算的结果
        //开始运算: 两数对比各位进行运算
        for (int i = 1; i <= minLength; i++) {
            bitOperateResult = result[result.length - i] + Character.getNumericValue(numbersA[numbersA.length - i]) + Character.getNumericValue(numbersB[numbersB.length - i]);
//            System.out.println(bitOperateResult);
            result[result.length - i] = bitOperateResult % 10; //低位留余
            result[result.length - i - 1] = result[result.length - i - 1] + bitOperateResult / 10; //高位进
        }
        return convertIntArrayToString(result);
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String a = scanner.next();
        String b = scanner.next();
        System.out.println("a + b = " + plus(a, b));
    }
}

560
123
a + b = 683