diff --git a/src/8/12/group-anagrams.cpp b/src/8/12/group-anagrams.cpp
index 13ef38c..53af385 100644
--- a/src/8/12/group-anagrams.cpp
+++ b/src/8/12/group-anagrams.cpp
@@ -15,7 +15,7 @@ public:
             m[ns].push_back(std::move(strs[i]));
         }
         vector<vector<string>> ans;
-        for(auto s :m){
+        for(auto &s :m){
             ans.push_back(std::move(s.second));
         }
         return ans;