977(A,cpp): solve “Wrong Subtraction”

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

977/a.cpp

@@ -0,0 +1,86 @@
+#include <iostream>
+
+namespace helpers {
+
+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;
+}
+
+template <typename T>
+inline void answer(const T &ans) {
+  cout << ans << "\n";
+}
+
+}  // namespace helpers
+
+namespace {
+
+using namespace std;
+using namespace helpers;
+
+int decrease(int n, int k) {
+  while (k > 0) {
+    if (n % 10 != 0) {
+      auto steps = min(n % 10, k);
+
+      n -= steps;
+      k -= steps;
+    } else {
+      n /= 10;
+      --k;
+    }
+  }
+
+  return n;
+}
+
+void solve() {
+  int n, k;
+  cin >> n >> k;
+
+  answer(decrease(n, k));
+}
+
+}  // namespace
+
+// for single test case, comment out for ‹N› test cases
+#define SINGLE
+
+#ifdef TEST
+
+#include "../.common/cpp/catch_amalgamated.hpp"
+
+TEST_CASE("examples") {
+  CHECK(decrease(512, 4) == 50);
+  CHECK(decrease(1000000000, 9) == 1);
+}
+
+#else
+
+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;
+}
+
+#endif