546(A,cpp): solve “Soldier and Bananas”

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

546/a.cpp

@@ -0,0 +1,66 @@
+#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 borrows(int k, int n, int w) {
+  int total = k * (1 + w) * w / 2;
+
+  return max(total - n, 0);
+}
+
+void solve() {
+  int k, n, w;
+  cin >> k >> n >> w;
+
+  cout << borrows(k, n, w) << "\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(borrows(3, 17, 4) == 13);
+  CHECK(borrows(3, 100, 4) == 0);
+}
+
+#endif