View Compilation Error

0_0_17677359_28383.cpp: In function 'long long int get_k(int, int)':
0_0_17677359_28383.cpp:50:18: error: invalid initialization of reference of type 'int&' from expression of type 'std::map<std::pair<int, int>, long long int>::mapped_type {aka long long int}'
     int& ans=mp[t];
                  ^