diff --git a/src/10/12/P3879.cpp b/src/10/12/P3879.cpp
new file mode 100644
index 0000000..bfab136
--- /dev/null
+++ b/src/10/12/P3879.cpp
@@ -0,0 +1,35 @@
+#include <cstdint>
+#include <iostream>
+#include <istream>
+#include <map>
+#include <set>
+#include <string>
+using ll = int64_t;
+
+ll n,m,l;
+std::map<std::string,std::set<ll>> s;
+std::string tmp;
+
+int main(){
+    std::iostream::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::cin>>n;
+    for(ll i=1;i<=n;i++){
+        std::cin>>l;
+        for(ll j=1;j<=l;j++){
+            std::cin>>tmp;
+            s[tmp].insert(i);
+        }
+    }
+    std::cin>>m;
+    while(m--){
+        std::cin>>tmp;
+        if(const auto p = s.find(tmp);p!=s.end()){
+            for(const ll i:p->second){
+                std::cout<<i<<" ";
+            }
+        }
+        std::cout<<"\n";
+    }
+}
\ No newline at end of file