Google Software Developer interview questions

The interview were 3 rounds, the second round was technical where i could not complete the 2nd problem and it was too hard , i could not complete the 2nd problem and it was too hard

1st round experience ............................................ Find the sum of K smallest element in all subarrays of size M. arr = [3, 1, 4, 5, 7, 8,11]; M=4, k=3 sum= [8, 10,16,20] i said correct brute force but on optimizing i was stuck using single multiset but then i got the intution of using 2 multiset one to store the smallest k and other for rest of elements.