Fast Power modulo & GCD

long long mod_pow(int a,int n,int p){    long long ret=1;    long long A=a;    while(n)    {        if (n & 1)            ret=(ret*A)%p;        A=(A*A)%p;        n>>=1;    }    return ret;}

Quick power modulo to prevent overflow in the middle:

Ll modular_multi (ll a, LL B, ll c) {// a * B % C ll res, temp; Res = 0, temp = A % C; while (B) {If (B & 1) {res + = temp; If (RES> = c) {res-= C ;}} temp <= 1; if (temp> = c) {temp-= C;} B >>= 1;} return res;} ll modular_exp (ll a, LL B, ll C) {// a ^ B % C cannot be changed to mod_pow, and an overflow occurs in the middle. The template still works like LL res, temp; Res = 1% C, temp = A % C; while (B) {If (B & 1) {res = modular_multi (Res, temp, c);} temp = modular_multi (temp, temp, C ); B >>= 1 ;}return res ;}

LL gcd(LL a, LL b) {    if (a < b) {        a ^= b, b ^= a, a ^= b;    }    if (b == 0) {        return a;    }    if (!(a & 1) && !(b & 1))        return gcd(a >> 1, b >> 1) << 1;    else if (!(b & 1))        return gcd(a, b >> 1);    else if (!(a & 1))        return gcd(a >> 1, b);    else        return gcd(b, a - b);}