876. 快速幂求逆元

https://www.acwing.com/problem/content/submission/code_detail/13591616/

AcWing/876/876.cpp

@@ -0,0 +1,35 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+int n, a, p;
+
+long long binpow(int a, int b, int m) {
+    long long res = 1;
+    a %= m;
+    while (b) {
+        if (b & 1) res = res * a % m;
+        a = 1ll * a * a % m;
+        b >>= 1;
+    }
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n;
+
+    while (n--) {
+        cin >> a >> p;
+        if (a % p) {
+            cout << binpow(a, p - 2, p) << endl;
+        } else {
+            cout << "impossible" << endl;
+        }
+    }
+
+    return 0;
+}