이슈 #357에서 솔루션 추가

Programmers/중복된_문자_제거.cpp

@@ -0,0 +1,19 @@
+#include <string>
+#include <vector>
+#include <unordered_set>
+
+using namespace std;
+
+string solution(string my_string) {
+    unordered_set<char> set;
+    string answer = "";
+
+    for (char c : my_string) {
+        if (set.find(c) == set.end()) {
+            set.insert(c);
+            answer += c;
+        }
+    }
+
+    return answer;
+}