LeetCode之字符串类

1 大数乘法

1.1 题目描述

https://leetcode.cn/problems/multiply-strings/

1.2 code

package org.example.atomicfieldupdater;

public class Multi {
    public static String multi(String a, String b) {
        if (a == null || b == null) {
            return "0";
        }
        if (a.equals("0") || b.equals("0")) {
            return "0";
        }
        String aa = new StringBuilder(a).reverse().toString();
        String bb = new StringBuilder(b).reverse().toString();

        String[] resultArr = new String[aa.length() + bb.length()];
        for (int i = 0; i < resultArr.length; i++) {
            resultArr[i] = "0";
        }

        int resultIndex = 0;
        int carry = 0;

        for (int i = 0; i < aa.length(); i++) {
            int tempA = aa.charAt(i) - '0';
            resultIndex = i;
            for (int j = 0; j < bb.length(); j++) {
                int tempB = bb.charAt(j) - '0';
                int tempRes = tempA * tempB + carry + Integer.parseInt(resultArr[resultIndex]);
                if (tempRes < 10) {
                    resultArr[resultIndex] = String.valueOf(tempRes);
                    resultIndex++;
                    carry = 0;
                } else {
                    resultArr[resultIndex] = String.valueOf(tempRes % 10);
                    resultIndex++;
                    carry = tempRes / 10;
                }
            }
            if (carry > 0) {
                resultArr[resultIndex++] = String.valueOf(carry);
                carry = 0;
            }
        }

        StringBuilder builer = new StringBuilder();
        for (int i = 0; i < resultIndex; i++) {
            builer.append(resultArr[i]);
        }

        return builer.reverse().toString();
    }

    public static void main(String[] args) {
//        System.out.println(multi("33", "5"));
//        System.out.println(multi("33", "0"));
//        System.out.println(multi("33", "33"));
//        System.out.println(multi("33", "333"));
//        System.out.println(multi("99", "999"));
//        System.out.println(multi("3", "2"));
        System.out.println(multi("123", "456"));
        System.out.println(multi("21", "83"));
        System.out.println(multi("218", "836"));
        System.out.println(multi("1000000000", "1000000000"));
    }
}