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Андрей
Asked:2022-02-01 09:39:16 +0000 UTC2022-02-01 09:39:16 +0000 UTC

长算术阶乘和位数

  • 772

有必要实现一个算法来找到 300!, 3000!, 10000! 的阶乘！在 C++ 中并找出位数

c++

1 个回答

  1. Best Answer
    #define USE_MATH_DEFINES_
#include <iostream>
#include <vector>
#include <string>
#include <cmath>
using namespace std;

int numberFactorial(const int n)
{
    return ceil(log10(M_PI * M_E * n) / 2 + n * log10(n / M_E));
}

int bar(int currSize, int x, vector<int>&arr)
{
    int curr = 0;
    for(size_t i = 0; i < currSize; ++i)
    {
        int prod = arr[i] * x + curr;
        arr[i] = prod % 10;
        curr = prod / 10;
    }
    while(curr)
    {
        arr[currSize] = curr % 10;
        curr /= 10;
        ++currSize;
    }
    return currSize;
}


string longFactorial(const int n)
{
    int currSize = 1;
    string res;
    vector<int>arr(numberFactorial(n),0);
    arr[0] = 1;
    for(size_t i = 2; i <= n; ++i)
    {
        currSize = bar(currSize, i, arr);
    }
    for(int i = currSize - 1; i >= 0; --i)
    {
        res += (arr[i] + 0x30);
    }
    return res;
}


int main(void)
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n; cin >> n;
    cout << numberFactorial(n) << endl;
    cout << longFactorial(n) << endl;

    
    cin.get();
    return EXIT_SUCCESS;
}
    • -6

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