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Consider without modulo. a = bx, so to solve for x, x = a/b. Unfortunately we can't really divide under modulo, but we can write this equation as a * b^-1 = x or x is a times the multiplicative inverse of b.
Luckily we can find the mulitplicative inverse of b under modulo M (because M=10^9 + 7 is prime, so b | b < M is coprime to M). We can calculate it by (b^(M-2))%M
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Simple One
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Consider without modulo.
a = bx, so to solve for x,x = a/b. Unfortunately we can't really divide under modulo, but we can write this equation asa * b^-1 = xor x is a times the multiplicative inverse of b.Luckily we can find the mulitplicative inverse of b under modulo M (because
M=10^9 + 7is prime, sob | b < Mis coprime to M). We can calculate it by(b^(M-2))%M