Some people are standing in a row in a park. There are trees between them which cannot be moved. Your task is to rearrange the people by their heights in a non-descending order without moving the trees. People can be very tall!
For a = [-1, 150, 190, 170, -1, -1, 160, 180], the output should be solution(a) = [-1, 150, 160, 170, -1, -1, 180, 190].