P1303. A*B Problem

发表于 2023-09-30 更新于 2023-10-25 分类于洛谷阅读次数： Waline：本文字数： 237 阅读时长 ≈ 1 分钟

考点

高精度

题解

#include <bits/stdc++.h>

using namespace std;

const int LEN = 5050;

class BigInt
{
public:
    int len_;
    int arr_[LEN];
    int &operator[](int idx)
    {
        return arr_[idx];
    }
    BigInt(string s = "")
    {
        memset(arr_, 0, sizeof(arr_));
        len_ = s.length();
        for (int i = 1; i <= len_; ++i)
        {
            arr_[i] = s[len_ - i] - '0';
        }
    }
    void flatten(int len)
    {
        len_ = len;
        for (int i = 1; i <= len_; ++i)
        {
            if (arr_[i] >= 10)
            {
                arr_[i + 1] += arr_[i] / 10;
                arr_[i] %= 10;
            }
        }
        while (!arr_[len_])
            --len_;
    }
    void print()
    {
        for (int i = max(1, len_); i >= 1; --i)
        {
            cout << arr_[i];
        }
    }
};

BigInt operator*(BigInt a, BigInt b)
{
    BigInt c;
    for (int i = 1; i <= a.len_; ++i)
    {
        for (int j = 1; j <= b.len_; ++j)
        {
            c[i + j - 1] += a[i] * b[j];
        }
    }
    //乘法的结果位数
    c.flatten(a.len_ + b.len_);
    return c;
}

int main()
{
    string a, b;
    cin >> a >> b;
    (BigInt(a) * BigInt(b)).print();
    return 0;
}