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108 lines
2.5 KiB
Python
108 lines
2.5 KiB
Python
"""
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R. Tarjan, Enumeration of the elementary circuits of a directed graph, SIAM Journal on Computing, 2 (1973), pp. 211-216
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procedure circuit_enumeration;
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begin
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procedure BACKTRACK(integer value v, logical result f);
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begin
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logical g;
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f := false;
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place v on point stack;
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mark(v) := true;
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place v on marked stack;
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for w in A(v) do
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if w<s then delete w from A(v);
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else if w=s then
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begin
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output circuit from s to v to s given by point stack
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f:=true;
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end;
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else if not mark(w) then
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begin
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BACKTRACK(w,g);
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f:=f or g;
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end;
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comment f=true if an elementary circuit continuing the
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partial path on the stack has been found;
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if f=true then
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begin
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while top of marked stack is not v do
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begin
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u:=top of marked stack;
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delete u from marked stack;
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mark(u):=false
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end;
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delete v from marked stack;
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mar(v):=false;
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end;
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delete v from point stack;
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end;
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integer n;
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for i:=1 until v do mark(i):=false;
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for s:=1 until v do
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begin
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BACKTRACK(s,flag);
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while marked stack not empty do
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begin
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u:=top of marked stack;
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mark(u):=false;
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delete u from marked stack;
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end;
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end;
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end;
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"""
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A = [[] for a in range(5)]
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A[0].append(1)
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A[0].append(4)
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A[1].append(4)
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A[2].append(0)
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A[2].append(3)
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A[2].append(4)
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A[3].append(0)
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A[3].append(2)
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A[3].append(4)
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A[4].append(3)
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def print_point_stack():
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for p in point_stack:
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print p,
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print
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point_stack = list()
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marked = dict()
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marked_stack = list()
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def backtrack(v, f):
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g = [False]
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f[0] = False
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point_stack.append(v)
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marked[v] = True
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marked_stack.append(v)
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for w in A[v]:
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if w<s:
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A[w] = 0
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elif w==s:
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print_point_stack()
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f[0] = True
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elif not marked[w]:
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backtrack(w, g)
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f[0] = f[0] or g[0]
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if f:
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while marked_stack[-1] != v:
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u = marked_stack.pop()
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marked[u] = False
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marked_stack.pop()
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marked[v] = False
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point_stack.pop()
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for i in range(len(A)):
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marked[i] = False
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for s in range(len(A)):
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backtrack(s, [False])
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while marked_stack:
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u = marked_stack.pop()
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marked[u] = False
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