基于公共值合并表示图边的元组列表

Question

I am attempting to write some python code that if given a list of tuples representing directed edges on a graph, I return all the possible paths. The graph, in this case, will not contain a cycle and each one of the nodes of the graph can only connect to one other node. The input would be in the form

[(1909, 1910), (1910, 1900), (1922, 1920), (1935,1922), (1940, 1939)]

and should return something in the form of

[(1909,1910,1900), (1935,1922,1920), (1940,1939)]

I'm not sure how to go about this cause the order must be maintained, ie because 1922 comes before 1920 and 1935 comes before 1922, the resulting answer must be (1935,1922,1920)

Any ideas on how to achieve this?

Answer 1

You can convert the tuples to a dictionary keyed on the first item and then progressively merge the items by linking the last element of each item.

tuples = [(1909, 1910), (1910, 1900), (1922, 1920), (1935,1922), (1940, 1939)]

links = { a:[b] for a,b in tuples }
while True:
    toMerge = [(a,bs[-1]) for a,bs in links.items() if bs[-1] in links]
    for a,b in toMerge:
        links[a].append(b)
        del links[b]
    else: break
result = [ [a,*bs] for a,bs in links.items() ]
print(result)

# [[1909, 1910, 1910], [1935, 1922, 1922], [1940, 1939]]