serialization - All permutations of a tree -


i need algorithm computes all possible permutations of given tree structure, example: 

4      3    \     |     \    2    \  /       1

this means, (4) needs ordered before (1), (3) before (2) , (2) before (1).thus output should contain of , not more following:

[4,3,2,1]   [3,4,2,1]   [3,2,4,1]

an invalid order example

[4,2,3,1]

as (2) before (3), (2) successor of (3) in graph. computing permutations , filtering invalid orderings doesn't work reasons of efficiency.

i don't need exact code, idea of how done helpful.

this problem topological sort directed graph.
resolved dfs time complexity o(e+v).
http://en.wikipedia.org/wiki/topological_sorting


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