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Update exgcd.cc

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Ariel 2024-02-19 16:53:47 +08:00 committed by GitHub
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number/exgcd.cc
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@ -50,6 +50,10 @@ namespace Exgcd {
// find the minimal non-negative integral solution of `ax = b (mod n)` // find the minimal non-negative integral solution of `ax = b (mod n)`
optional<ll> congruential(ll a, ll b, ll n) { optional<ll> congruential(ll a, ll b, ll n) {
if (a == 0) {
if (b != 0) return nullopt;
return 0;
}
if (a < 0 && a != LLONG_MIN && b != LLONG_MIN) a = -a, b = -b; if (a < 0 && a != LLONG_MIN && b != LLONG_MIN) a = -a, b = -b;
auto sol = diophantine(a, n, b); auto sol = diophantine(a, n, b);
if (sol == nullopt) { if (sol == nullopt) {