간단한 exgcd
1. exgcdtuple extendedGCD(ll a, ll b) { // ax + by = gcd(a, b) if (b == 0) return {1, 0, a}; auto [x2, y2, g] = extendedGCD(b, a % b); return {y2, x2 - (a / b) * y2, g};}베주항등식 $ax_1 + by_1 = g$ 는 항상 해 존재$let)~ a=bk+r$$(bk + r)x_1 + by_1 = g$$b(kx_1+y_1) + rx_1 = g$$let)~ x_2 = kx_1+y_1, y_2=x_1$$\therefore x_1=y_2, y_1 = x_2-ky_2$2. modular inversell modInverse(ll a, ll b) { // a^-1 mod..