oddluck-limnoria-plugins/WordGames/trie.py

###
# Copyright (c) 2012, Mike Mueller
# Copyright (c) 2020, oddluck <oddluck@riseup.net>
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"""
Quick & dirty prefix tree (aka trie).
"""

# This got a little uglier because using a nice object-oriented approach took
# too much time and memory on big trees.  Now every node is simply a dict,
# with the special '*' field meaning that the word is complete at that node.


class Trie(object):
    def __init__(self):
        self.contents = {"*": False}

    def add(self, value, contents=None):
        if contents is None:
            contents = self.contents
        if not value:
            contents["*"] = True
            return
        prefix = value[0]
        remainder = value[1:]
        child_contents = contents.get(prefix, None)
        if not child_contents:
            child_contents = {"*": False}
            contents[prefix] = child_contents
        self.add(remainder, child_contents)

    def find(self, value):
        "Return true if the value appears, false otherwise."
        x = self.find_prefix(value)
        return x and x["*"] == True

    def find_prefix(self, value, contents=None):
        "Return true if the given prefix appears in the tree."
        if contents is None:
            contents = self.contents
        if not value:
            return contents
        child_contents = contents.get(value[0], None)
        if not child_contents:
            return None
        return self.find_prefix(value[1:], child_contents)

    def dump(self, indent=0, contents=None):
        "Dump the trie to stdout."
        if contents is None:
            contents = self.contents
        for key in sorted(contents.keys()):
            if key == "*":
                continue
            text = indent * " "
            text += key
            child_contents = contents[key]
            if child_contents["*"]:
                text += "*"
            print(text)
            self.dump(indent + 2, child_contents)


if __name__ == "__main__":
    import resource
    import sys
    import time

    if "--perf" in sys.argv:
        # Performance test, last arg should be input file
        start = time.time()
        t = Trie()
        f = open(sys.argv[-1], "r")
        for line in f:
            t.add(line.strip())
        mem = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
        elapsed = time.time() - start
        print("Trie created in %g seconds." % elapsed)
        print("Used %dMB RAM." % (mem / 1024))
    else:
        # Regular sanity test
        t = Trie()
        t.add("hell")
        t.add("hello")
        t.add("he")
        t.add("world")
        t.add("alphabet")
        t.add("foo")
        t.add("food")
        t.add("foodie")
        t.add("bar")
        t.add("alphanumeric")
        t.dump()

        assert not t.find("h")
        assert t.find("he")
        assert not t.find("hel")
        assert t.find("hell")
        assert t.find("hello")
        assert not t.find("r")
        assert t.find("world")
        assert not t.find("ba")
        assert t.find("bar")
        assert t.find("alphabet")
        assert t.find("alphanumeric")
        assert not t.find("alpha")
        assert not t.find("f")
        assert not t.find("fo")
        assert t.find("foo")
        assert t.find("food")
        assert not t.find("foodi")
        assert t.find("foodie")