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Add doctests to networking_flow/minimum_cut.py (#1126)

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Christian Clauss 2019-08-13 11:59:49 +02:00 committed by GitHub
parent c74fd0c9bf
commit dc2b575274
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1 changed files with 32 additions and 25 deletions
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43
networking_flow/minimum_cut.py
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@ -1,10 +1,19 @@
# Minimum cut on Ford_Fulkerson algorithm. # Minimum cut on Ford_Fulkerson algorithm.
test_graph = [
[0, 16, 13, 0, 0, 0],
[0, 0, 10, 12, 0, 0],
[0, 4, 0, 0, 14, 0],
[0, 0, 9, 0, 0, 20],
[0, 0, 0, 7, 0, 4],
[0, 0, 0, 0, 0, 0],
]
def BFS(graph, s, t, parent): def BFS(graph, s, t, parent):
# Return True if there is node that has not iterated. # Return True if there is node that has not iterated.
visited = [False]*len(graph) visited = [False] * len(graph)
queue=[] queue = [s]
queue.append(s)
visited[s] = True visited[s] = True
while queue: while queue:
@ -17,25 +26,29 @@ def BFS(graph, s, t, parent):
return True if visited[t] else False return True if visited[t] else False
def mincut(graph, source, sink): def mincut(graph, source, sink):
# This array is filled by BFS and to store path """This array is filled by BFS and to store path
parent = [-1]*(len(graph)) >>> mincut(test_graph, source=0, sink=5)
[(1, 3), (4, 3), (4, 5)]
"""
parent = [-1] * (len(graph))
max_flow = 0 max_flow = 0
res = [] res = []
temp = [i[:] for i in graph] # Record orignial cut, copy. temp = [i[:] for i in graph] # Record orignial cut, copy.
while BFS(graph, source, sink, parent) : while BFS(graph, source, sink, parent):
path_flow = float("Inf") path_flow = float("Inf")
s = sink s = sink
while(s != source): while s != source:
# Find the minimum value in select path # Find the minimum value in select path
path_flow = min (path_flow, graph[parent[s]][s]) path_flow = min(path_flow, graph[parent[s]][s])
s = parent[s] s = parent[s]
max_flow += path_flow max_flow += path_flow
v = sink v = sink
while(v != source): while v != source:
u = parent[v] u = parent[v]
graph[u][v] -= path_flow graph[u][v] -= path_flow
graph[v][u] += path_flow graph[v][u] += path_flow
@ -44,16 +57,10 @@ def mincut(graph, source, sink):
for i in range(len(graph)): for i in range(len(graph)):
for j in range(len(graph[0])): for j in range(len(graph[0])):
if graph[i][j] == 0 and temp[i][j] > 0: if graph[i][j] == 0 and temp[i][j] > 0:
res.append((i,j)) res.append((i, j))
return res return res
graph = [[0, 16, 13, 0, 0, 0],
[0, 0, 10 ,12, 0, 0],
[0, 4, 0, 0, 14, 0],
[0, 0, 9, 0, 0, 20],
[0, 0, 0, 7, 0, 4],
[0, 0, 0, 0, 0, 0]]
source, sink = 0, 5 if __name__ == "__main__":
print(mincut(graph, source, sink)) print(mincut(test_graph, source=0, sink=5))