/in/foo.cc: In function 'int helper(std::vector<int>&)':
/in/foo.cc:24:5: error: 'stack' was not declared in this scope
     stack<int> stk;
     ^~~~~
/in/foo.cc:24:11: error: expected primary-expression before 'int'
     stack<int> stk;
           ^~~
/in/foo.cc:26:16: error: 'stk' was not declared in this scope
         while(!stk.empty() && row[stk.top()] >= row[i]) {
                ^~~
/in/foo.cc:29:13: error: 'stk' was not declared in this scope
         if(!stk.empty()) {
             ^~~
/in/foo.cc:32:9: error: 'stk' was not declared in this scope
         stk.push(i);
         ^~~
/in/foo.cc:34:5: error: 'stk' was not declared in this scope
     stk = stack<int>();
     ^~~
/in/foo.cc:34:17: error: expected primary-expression before 'int'
     stk = stack<int>();
                 ^~~