이슈 #363에서 솔루션 추가

Programmers/한_번만_등장한_문자.cpp

@@ -0,0 +1,22 @@
+#include <string>
+#include <vector>
+#include <map>
+
+using namespace std;
+
+string solution(string s) {
+    map<char, int> map;
+    string answer = "";
+
+    for (char c : s) {
+        map[c]++;
+    }
+
+    for (const auto& it : map) {
+        if (it.second == 1) {
+            answer += it.first;
+        }
+    }
+
+    return answer;
+}