Python to Java translation

Question

i get quite short code of algorithm in python, but i need to translate it to Java. I didnt find any program to do that, so i will really appreciate to help translating it.

I learned python a very little to know the idea how algorithm work.

The biggest problem is because in python all is object and some things are made really very confuzing like

sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source))

and "self.adj" is like hashmap with multiple values which i have no idea how to put all together. Is any better collection for this code in java?

code is:

class FlowNetwork(object):
    def __init__(self):
        self.adj, self.flow, = {},{}

    def add_vertex(self, vertex):
        self.adj[vertex] = []

    def get_edges(self, v):
        return self.adj[v]

    def add_edge(self, u,v,w=0):
        self.adj[u].append((v,w))
        self.adj[v].append((u,0))
        self.flow[(u,v)] = self.flow[(v,u)] = 0

    def find_path(self, source, sink, path):
        if source == sink:
            return path
        for vertex, capacity in self.get_edges(source):
            residual = capacity - self.flow[(source,vertex)]
            edge = (source,vertex,residual)
            if residual > 0 and not edge in path:
                result = self.find_path(vertex, sink, path + [edge])
                if result != None:
                    return result

    def max_flow(self, source, sink):
        path = self.find_path(source, sink, [])
        while path != None:
            flow = min(r for u,v,r in path)
            for u,v,_ in path:
                self.flow[(u,v)] += flow
                self.flow[(v,u)] -= flow
                path = self.find_path(source, sink, [])
        return sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source))
g = FlowNetwork()
map(g.add_vertex, ['s','o','p','q','r','t'])
g.add_edge('s','o',3)
g.add_edge('s','p',3)
g.add_edge('o','p',2)
g.add_edge('o','q',3)
g.add_edge('p','r',2)
g.add_edge('r','t',3)
g.add_edge('q','r',4)
g.add_edge('q','t',2)
print g.max_flow('s','t')

result of this example is "5".

algorithm find max flow in graph(linked list or whatever) from source vertex "s" to destination "t".

Many thanks for any idea

Answer 1

Java doesn't have anything like Python's comprehension syntax. You'll have to replace it with code that loops over the list and aggregates the value of sum as it goes.

Also, self.flow looks like a dictionary indexed by pairs. The only way to match this, AFAIK, is to create a class with two fields that implements hashCode and equals to use as a key for a HashMap.