NEFU 84 五指山

题目链接：http://acm.nefu.edu.cn/JudgeOnline/problem/84.jsp

思路：与上一题很相似，扩展欧几里得算法。

#include <iostream>#include <cstdlib>#include <cstdio>#include <cstring>#include <string>using namespace std;typedef long long LL;LL n, m, ax, by;void ex_gcd(LL a, LL b, LL &d, LL &x, LL &y){if(!b){d = a; x = 1; y = 0;}else{ex_gcd(b, a%b, d, y, x);y -= x*(a/b);}}void read_case(){scanf("%lld%lld%lld%lld", &n, &m, &ax, &by);}void solve(){read_case();LL d, x, y;ex_gcd(m, n, d, x, y);if((by-ax) % d) { printf("Impossible\n"); return ;}LL b1 = n / d;x *= (by-ax) / d;LL ans = (x % b1 + b1) % b1;printf("%lld\n", ans);}int main(){int T;scanf("%d", &T);while(T--){solve();}return 0;}