Fast Power PowerMod

     When I was brushing the questions before, I achieved fast power, I was confused, and the competition was approaching. Although I was not as strong as my seniors (called me scumming), we can't just give up. After all, this is also the testimony of my one-semester study! Today, I will summarize the problem of fast power.

    The meaning of the question is very simple: give you a number x, ask it to calculate the value of its y power modulo p! That is x^y%b

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    // Implement fast power by recursion

    int PW (int x, int y, int p) {

        if(!y){

            return 1;

        }

        int res=PW（x,y/2,p）*PW（x,y/2,p）%p;

        if(y&1==0){//That is, y is the base

                res=res*x%p;

        }

        return res;

    }

    

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The value of a can be reduced by this formula

int PowerMod(int a,int b,int c){

       int res=1;

        a=a%c;

        while(b>0){

                if(b%2==1){//When b is odd

                         res = res * a% c;

                }

                b/=2;

                a=a*a%c;

        }


        return res;

}

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