791(A,cpp): solve “Bear and Big Brother”

Signed-off-by: Matej Focko <me@mfocko.xyz>

791/a.cpp

@@ -0,0 +1,81 @@
+#include <iostream>
+
+namespace {
+
+using namespace std;
+
+long pow(long base, long exp) {
+  if (exp == 0)
+    return 1;
+  long half = pow(base, exp / 2);
+  if (exp % 2 == 0)
+    return half * half;
+  return half * half * base;
+}
+
+int find_k(int a, int b) {
+  int lower = 1;
+  int upper = 7;
+
+  while (lower <= upper) {
+    int mid = (lower + upper) / 2;
+
+    int new_a = a * pow(3, mid);
+    int new_b = b * pow(2, mid);
+
+    if (new_a <= new_b) {
+      lower = mid + 1;
+    } else {
+      upper = mid - 1;
+    }
+  }
+
+  return lower;
+}
+
+void solve() {
+  int a, b;
+  cin >> a >> b;
+
+  cout << find_k(a, b) << "\n";
+}
+
+} // namespace
+
+// for single test case, comment out for ‹N› test cases
+#define SINGLE
+
+#ifndef TEST
+
+int main(void) {
+
+#ifdef SINGLE
+
+  solve();
+
+#else
+
+  // for multiple test cases
+  int N;
+  std::cin >> N >> std::ws;
+
+  for (auto i = 0; i < N; ++i) {
+    solve();
+  }
+
+#endif
+
+  return 0;
+}
+
+#else
+
+#include "../.common/cpp/catch_amalgamated.hpp"
+
+TEST_CASE("examples") {
+  CHECK(find_k(4, 7) == 2);
+  CHECK(find_k(4, 9) == 3);
+  CHECK(find_k(1, 1) == 1);
+}
+
+#endif