MDantas's blog

By MDantas, 11 years ago, In English

Given four integers N,M,x,y ( 1 <= x,y,N,M <= 10^9 ), what's the minimum value of T such that:

T ≡ x mod N

T ≡ y mod M

Can somebody help me?

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11 years ago, # |
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    11 years ago, # ^ |
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    How can I use Chinese Remainder Theorem when N,M aren't coprimes ?

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      11 years ago, # ^ |
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      You can calculate D = GCD(N, M) and the remainders modulo D, N / D, M / D, and then you'll just need to solve the resulting congruence (if x mod D != y mod D, then, obviously, there is no solution).

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        11 years ago, # ^ |
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        T*(d^-1) ≡ x/d mod N/d

        T*(d^-1) ≡ y/d mod M/d

        This way ?

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          11 years ago, # ^ |
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          Just T ≡ (x % D) mod D, T ≡ (y % D) mod D, T ≡ (x % (N / D)) mod (N / D), T ≡ (y % (M / D)) mod (M / D)

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11 years ago, # |
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T=N*k+x, T=M*p+y => N*k+x=M*p+y <=> N*k-M*p=y-x. Now it's Extended Euclid's algorithm problem. Use it to find k and p.