P4777 【模板】扩展中国剩余定理（EXCRT）

https://www.luogu.com.cn/record/89726444

Luogu/P4777/P4777.cpp

@@ -0,0 +1,64 @@
+#include <iostream>
+#include <algorithm>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n;
+long long a1, b1, a2, b2;
+
+long long exgcd(long long a, long long b, long long& x, long long& y) {
+    if (!b) {
+        x = 1;
+        y = 0;
+        return a;
+    }
+
+    long long g = exgcd(b, a % b, y, x);
+    y -= a / b * x;
+    return g;
+}
+
+long long lcm(long long a, long long b) {
+    return a / std::__gcd(a, b) * b;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        // $x \equiv a_i (mod b_i)$
+        cin >> a2 >> b2;
+
+        if (i == 1) {
+            a1 = a2;
+            b1 = b2;
+        } else {
+            long long x, y,
+                g = exgcd(a1, a2, x, y),
+                c = b2 - b1,
+                m1 = a2 / g,
+                m2 = lcm(a1, a2);
+
+            if (c % g) {
+                cout << -1 << endl;
+
+                exit(0);
+            }
+
+            x = (static_cast<__int128>(x) * c / g % m1 + m1) % m1;
+            b1 = ((a1 * x + b1) % m2 + m2) % m2;
+            a1 = m2;
+        }
+    }
+
+    cout << b1 % a1 << endl;
+
+    return 0;
+}