problems(cpp): add „383. Ransom Note“

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/ransom-note.cpp

@@ -0,0 +1,53 @@
+#include <cassert>
+#include <map>
+#include <string>
+
+namespace {
+
+std::map<char, int> build_freqs(const std::string& input)
+{
+    std::map<char, int> freqs;
+
+    for (auto c : input) {
+        freqs[c]++;
+    }
+
+    return freqs;
+}
+
+bool subtract(std::map<char, int> available, const std::string& message)
+{
+    for (auto c : message) {
+        available[c]--;
+
+        if (available[c] < 0) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+}
+
+class Solution {
+public:
+    bool canConstruct(const std::string& ransomNote, const std::string& magazine)
+    {
+        auto available = build_freqs(magazine);
+        return subtract(available, ransomNote);
+    }
+};
+
+int main()
+{
+    Solution s;
+
+    assert(!s.canConstruct("a", "b"));
+    assert(!s.canConstruct("aa", "ab"));
+    assert(s.canConstruct("aa", "aab"));
+    assert(s.canConstruct("ab", "aab"));
+    assert(s.canConstruct("ba", "aab"));
+
+    return 0;
+}