牛客 求整数的阶乘 高精度乘法模板

高精度乘法模板

string mul(string A, string B) {
	string ret(A.length() + B.length()+1, 0);
	for(auto& ch : A) ch -= '0';
	for(auto& ch : B) ch -= '0';
	reverse(A.begin(), A.end());
	reverse(B.begin(), B.end());
	int pos, flag; //flag进位标志
	for(int i=0; i<(int)A.length(); i++) {
		pos = i, flag = 0;
		for(int j=0; j<(int)B.length(); j++, pos++) {
			int t = (A[i] * B[j]) + flag + ret[pos];
			flag = t / 10;
			ret[pos] = t % 10;
		}
		ret[pos] += flag;
	}
	while(ret.back() == 0) ret.pop_back();
	for(auto& ch : ret) ch += '0';
	reverse(ret.begin(), ret.end());
	return ret;
}

完整代码

#ifdef debug
#include <time.h>
#include "/home/majiao/mb.h"
#endif

#include <iostream>
#include <algorithm>
#include <vector>
#include <string.h>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <math.h>

#define MAXN ((int)1e5+7)
#define ll long long int
#define INF (0x7f7f7f7f)
#define fori(lef, rig) for(int i=lef; i<=rig; i++)
#define forj(lef, rig) for(int j=lef; j<=rig; j++)
#define fork(lef, rig) for(int k=lef; k<=rig; k++)
#define QAQ (0)

using namespace std;

#define show(x...) \ do { \ cout << "\033[31;1m " << #x << " -> "; \ err(x); \ } while (0)

void err() { cout << "\033[39;0m" << endl; }
template<typename T, typename... A>
void err(T a, A... x) { cout << a << ' '; err(x...); }

namespace FastIO{

	char print_f[105];
	void read() {}
	void print() { putchar('\n'); }

	template <typename T, typename... T2>
		inline void read(T &x, T2 &... oth) {
			x = 0;
			char ch = getchar();
			ll f = 1;
			while (!isdigit(ch)) {
				if (ch == '-') f *= -1; 
				ch = getchar();
			}
			while (isdigit(ch)) {
				x = x * 10 + ch - 48;
				ch = getchar();
			}
			x *= f;
			read(oth...);
		}
	template <typename T, typename... T2>
		inline void print(T x, T2... oth) {
			ll p3=-1;
			if(x<0) putchar('-'), x=-x;
			do{
				print_f[++p3] = x%10 + 48;
			} while(x/=10);
			while(p3>=0) putchar(print_f[p3--]);
			putchar(' ');
			print(oth...);
		}
} // namespace FastIO
using FastIO::print;
using FastIO::read;

int n, m, Q, K;

string strmul(string s1,string s2){
    string str(s1.size()+s2.size(),'0');
    reverse(s1.begin(),s1.end());
    reverse(s2.begin(),s2.end());
    int k,up;
    for(int i=0;i<(int)s1.size();i++){
        k=i;
        up=0;
        for(int j=0;j<(int)s2.size();j++,k++){
            int t=(s1[i]-'0')*(s2[j]-'0')+up+str[k]-'0';
            up=t/10;
            str[k]=t%10+'0';
        }
        str[k]=up+'0';
    }
    k=str.size()-1;
    while(str[k]=='0')
        str.pop_back();
    reverse(str.begin(),str.end());
    return str;
}

string mul(string A, string B) {
	string ret(A.length() + B.length()+1, 0);
	for(auto& ch : A) ch -= '0';
	for(auto& ch : B) ch -= '0';
	reverse(A.begin(), A.end());
	reverse(B.begin(), B.end());
	int pos, flag; //flag进位标志
	for(int i=0; i<(int)A.length(); i++) {
		pos = i, flag = 0;
		for(int j=0; j<(int)B.length(); j++, pos++) {
			int t = (A[i] * B[j]) + flag + ret[pos];
			flag = t / 10;
			ret[pos] = t % 10;
		}
		ret[pos] += flag;
	}
	while(ret.back() == 0) ret.pop_back();
	for(auto& ch : ret) ch += '0';
	reverse(ret.begin(), ret.end());
	return ret;
}

int main() {
#ifdef debug
	freopen("test", "r", stdin);
	clock_t stime = clock();
#endif
	cin >> n;
	string ret = "1";
	for(int i=1; i<=n; i++) {
		ret = mul(ret, to_string(i));
	}
	cout << ret << endl;





#ifdef debug
	clock_t etime = clock();
	printf("rum time: %lf 秒\n",(double) (etime-stime)/CLOCKS_PER_SEC);
#endif 
	return 0;
}