Write a function that returns all possible topological sorts of a directed acyclic graph (DAG). The graph will be given as an adjacency list.

``` def all_topological_sorts(graph): from collections import defaultdict def backtrack(visited, path, results): if len(path) == len(graph): results.append(path[:]) return for i in range(len(graph)): if not visited[i] and not any(visited[neigh] for neigh in graph[i]): visited[i] = True path.append(i) backtrack(visited, path, results) path.pop() visited[i] = False results = [] backtrack([False] * len(graph), [], results) return results ```