大整数相乘-优快云博客

本文链接：https://blog.youkuaiyun.com/jtss123/article/details/137202893

文章介绍了使用C++实现大整数乘法的方法，通过递归创建vector数组并处理进位，适用于处理大整数乘法问题。

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大整数*小数字

vector<int> mul(vector<int> a, int b)
{
    vector<int> c;
    for (int i = 0, t = 0; i < a.size() || t; i++)
    {
        if (i < a.size())
            t += a[i] * b; // 一次性乘完
        c.push_back(t % 10);
        t /= 10;
    }
    return c;
}

大整数*大整数

思路继续创一个vector数组，此时不是一次性存储的，要用res[i+j]存储上次运算得出的结果

vector<int> mult(vector<int> a, vector<int> b)
{
    vector<int> res(a.size() + b.size(), 0);
    for (int i = 0; i < a.size(); i++)
    {
        int carry = 0;
        for (int j = 0; j < b.size() || carry; j++)
        {
            int t = res[i + j] + (j < b.size() ? a[i] * b[j] : 0) + carry;
            res[i + j] = t % 10;
            carry = t / 10;
        }
    }
    while (res.back() == 0 && res.size() >= 1)
    {
        res.pop_back();
    }
    return res;
}

#include <bits/stdc++.h>
using namespace std;
vector<int> mul(vector<int> a, int b)
{
    vector<int> c;
    for (int i = 0, t = 0; i < a.size() || t; i++)
    {
        if (i < a.size())
            t += a[i] * b; // 一次性乘完
        c.push_back(t % 10);
        t /= 10;
    }
    return c;
}
vector<int> mult(vector<int> a, vector<int> b)
{
    vector<int> res(a.size() + b.size(), 0);
    for (int i = 0; i < a.size(); i++)
    {
        int carry = 0;
        for (int j = 0; j < b.size() || carry; j++)
        {
            int t = res[i + j] + (j < b.size() ? a[i] * b[j] : 0) + carry;
            res[i + j] = t % 10;
            carry = t / 10;
        }
    }
    while (res.back() == 0 && res.size() >= 1)
    {
        res.pop_back();
    }
    return res;
}
int main()
{
    string a;
    int b;
    string q;

    cin >> a >> q;
    vector<int> m, n;
    vector<int> res;
    for (int i = a.size() - 1; i >= 0; i--)
    {
        m.push_back(a[i] - '0');
    }
    for (int i = q.size() - 1; i >= 0; i--)
    {
        n.push_back(q[i] - '0');
    }
    res = mult(m, n);
    for (int i = res.size() - 1; i >= 0; i--)
    {
        cout << res[i];
    }
}