快速幂和快速乘

快速幂模板

ll power(ll a, ll b, ll p)
{
	ll ans = 1 % p, base = a;
	while (b)
	{
		if (b & 1)
		{
			ans = (ans%p * base%p) % p;
		}
		base = base* base%p;
		b >>= 1;
	}
	return ans;
}

快速乘模板

简单模板

ll quickMul(ll a, ll b, ll mod)
{
	ll res = 0;
	while (b)
	{
		if (b & 1) res = (res + a) % mod;
		a = (a + a) % mod;
		b >>= 1;
	}
	return res;
}

高效算法

ll mul(ll a, ll b, ll mod)
{
	a %= mod;
	b %= mod;
	ll res = 0;
	while (b)
	{
		if (b & 1)
		{
			res += a;
			if (res >= mod)
				res -= mod;
		}
		b >>= 1;
		a <<= 1;
		if (a >= mod)  a -= mod;
	}
	return res;
}

GCD模板

/*
递归的写法
*/
#include<cstdio>
using namespace std;
 
int gcd(int a,int b)
{
    return b>0?gcd(b,a%b):a;
}
 
int main()
{
    int a,b;
    while(scanf("%d%d",&a,&b)==2)
    {
        printf("%d\n",gcd(a,b));
    }
    return 0;
}