蓝桥杯 BASIC 30 阶乘计算（大数处理）

【思路】：大数基本都是这思路，采用数组或者字符串，每个数采用倒序的方式从头开始存储。每次进位进到下一位上。

【AC代码】：两个数组来回颠倒。

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <iomanip>
using namespace std;

#define MAX 3000

int cal(int *s,int len,int n,int *d)
{
	int i = 0,temp = 0;
	for (i = 0; i < len; i++)
	{
		temp = s[i] * n + temp;
		d[i] = temp%10;
		temp = temp/10;
	}
	while (temp)
	{
		d[i++] = temp%10;
		temp = temp/10;
	}
	return i;
}

void output(int *s,int len)
{
	int i = 0;
	while (len)
	{
		cout << s[--len];
	}
}

int main()
{
	//freopen("in.txt","r",stdin);
	//freopen("out.txt","w",stdout);
	int n =0,i = 0,j = 1,k = 0;
	int s1[MAX]={1},s2[MAX];
	cin >> n;
	for (i = 1; i <= n; i++)
	{
		if (j > 0)
		{
			k = cal(s1,j,i,s2);
			j = 0;
		}
		else
		{
			j = cal(s2,k,s1);
			k = 0;
		}
	}
	if (0 == n%2)
		output(s1,j);
	else
		output(s2,k);
}

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <iomanip>
using namespace std;

#define MAX 3000

int cal(int *s,int n)
{
	int i = 0,temp = 0;
	for (i = 0; i < len; i++)
	{
		temp = s[i] * n + temp;
		s[i] = temp%10;
		temp = temp/10;
	}
	while (temp)
	{
		s[i++] = temp%10;
		temp = temp/10;
	}
	return i;
}

void output(int *s,len = 1;
	int s1[MAX]={1};
	cin >> n;
	for (i = 1; i <= n; i++)
	{
		len = cal(s1,len,i);
	}
	output(s1,len);
}