def find_cycles(graph):
    # Record visited nodes in a set, which gives us constant-time lookup of
    # nodes.
    visited = set()
    cycles = []
    for node in graph:
        if node in visited:
            continue  # already been here
        find_cycles_from_node(graph, node, visited, cycles, [])
    return cycles

def find_cycles_from_node(graph, node, visited, cycles, path):
    if node in path:
        # We have found a cycle from the first occurrence of node
        # to here.
        # Remove prefix up to the first occurrence:
        index = path.index(node)
        cycle = path[index:]
        cycles.append(cycle)
        return

    visited.add(node)
    path.append(node)
    length = len(path)
    for neighbor in graph[node]:
        # Find cycles forward in graph.
        find_cycles_from_node(graph, neighbor, visited, cycles, path)
        # Crop path to prefix up to current node.
        path = path[:length]