pnc.sublime-snippet

<snippet>
	<content><![CDATA[
class PnC
{
public:
    vector<int>fact,invfact;
    PnC( int n )
    {
        fact.resize(n);
        invfact.resize(n);
        fact[0] = invfact[0] = 1;
        for(int i=1;i<n;i++)
        {
            fact[i] = (i * fact[i-1] )%MOD;
            invfact[i] = modinv( fact[i] );
        }
    }
    int modinv( int x)
    {
        return expo(x,MOD-2);
    }
    int expo(int base,int x)
    {
        int res = 1;    
        base = base % MOD; 
        while (x > 0)
        {
            if (x & 1)
                res = (res*base) % MOD;
            x= x>>1;
            base = (base*base) % MOD;  
        }
        return res;
    }
    int choose( int n, int k )
    {
        if( k < 0 || k > n ) return 0;
        int ans = fact[n];
        ans = (ans * invfact[n-k] )%MOD;
        ans = (ans * invfact[k])%MOD;
        return ans;
    }
};
]]></content>
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</snippet>