
from __future__ import division, print_function


__all__ = ['Counter']


try:
    from collections import Counter
except ImportError:
    from operator import itemgetter
    from heapq import nlargest
    from itertools import repeat, ifilter

    class Counter(dict):
        '''Dict subclass for counting hashable objects.  Sometimes called a bag
        or multiset.  Elements are stored as dictionary keys and their counts
        are stored as dictionary values.

        >>> Counter('zyzygy')
        Counter({'y': 3, 'z': 2, 'g': 1})

        '''

        def __init__(self, iterable=None, **kwds):
            '''Create a new, empty Counter object.  And if given, count elements
            from an input iterable.  Or, initialize the count from another mapping
            of elements to their counts.

            >>> c = Counter()                           # a new, empty counter
            >>> c = Counter('gallahad')                 # a new counter from an iterable
            >>> c = Counter({'a': 4, 'b': 2})           # a new counter from a mapping
            >>> c = Counter(a=4, b=2)                   # a new counter from keyword args

            '''
            self.update(iterable, **kwds)

        def __missing__(self, key):
            return 0

        def most_common(self, n=None):
            '''List the n most common elements and their counts from the most
            common to the least.  If n is None, then list all element counts.

            >>> Counter('abracadabra').most_common(3)
            [('a', 5), ('r', 2), ('b', 2)]

            '''
            if n is None:
                return sorted(self.iteritems(), key=itemgetter(1), reverse=True)
            return nlargest(n, self.iteritems(), key=itemgetter(1))

        def elements(self):
            '''Iterator over elements repeating each as many times as its count.

            >>> c = Counter('ABCABC')
            >>> sorted(c.elements())
            ['A', 'A', 'B', 'B', 'C', 'C']

            If an element's count has been set to zero or is a negative number,
            elements() will ignore it.

            '''
            for elem, count in self.iteritems():
                for _ in repeat(None, count):
                    yield elem

        # Override dict methods where the meaning changes for Counter objects.

        @classmethod
        def fromkeys(cls, iterable, v=None):
            raise NotImplementedError(
                'Counter.fromkeys() is undefined.  Use Counter(iterable) instead.')

        def update(self, iterable=None, **kwds):
            '''Like dict.update() but add counts instead of replacing them.

            Source can be an iterable, a dictionary, or another Counter instance.

            >>> c = Counter('which')
            >>> c.update('witch')           # add elements from another iterable
            >>> d = Counter('watch')
            >>> c.update(d)                 # add elements from another counter
            >>> c['h']                      # four 'h' in which, witch, and watch
            4

            '''
            if iterable is not None:
                if hasattr(iterable, 'iteritems'):
                    if self:
                        self_get = self.get
                        for elem, count in iterable.iteritems():
                            self[elem] = self_get(elem, 0) + count
                    else:
                        dict.update(self, iterable) # fast path when counter is empty
                else:
                    self_get = self.get
                    for elem in iterable:
                        self[elem] = self_get(elem, 0) + 1
            if kwds:
                self.update(kwds)

        def copy(self):
            'Like dict.copy() but returns a Counter instance instead of a dict.'
            return Counter(self)

        def __delitem__(self, elem):
            'Like dict.__delitem__() but does not raise KeyError for missing values.'
            if elem in self:
                dict.__delitem__(self, elem)

        def __repr__(self):
            if not self:
                return '%s()' % self.__class__.__name__
            items = ', '.join(map('%r: %r'.__mod__, self.most_common()))
            return '%s({%s})' % (self.__class__.__name__, items)

        # Multiset-style mathematical operations discussed in:
        #       Knuth TAOCP Volume II section 4.6.3 exercise 19
        #       and at http://en.wikipedia.org/wiki/Multiset
        #
        # Outputs guaranteed to only include positive counts.
        #
        # To strip negative and zero counts, add-in an empty counter:
        #       c += Counter()

        def __add__(self, other):
            '''Add counts from two counters.

            >>> Counter('abbb') + Counter('bcc')
            Counter({'b': 4, 'c': 2, 'a': 1})


            '''
            if not isinstance(other, Counter):
                return NotImplemented
            result = Counter()
            for elem in set(self) | set(other):
                newcount = self[elem] + other[elem]
                if newcount > 0:
                    result[elem] = newcount
            return result

        def __sub__(self, other):
            ''' Subtract count, but keep only results with positive counts.

            >>> Counter('abbbc') - Counter('bccd')
            Counter({'b': 2, 'a': 1})

            '''
            if not isinstance(other, Counter):
                return NotImplemented
            result = Counter()
            for elem in set(self) | set(other):
                newcount = self[elem] - other[elem]
                if newcount > 0:
                    result[elem] = newcount
            return result

        def __or__(self, other):
            '''Union is the maximum of value in either of the input counters.

            >>> Counter('abbb') | Counter('bcc')
            Counter({'b': 3, 'c': 2, 'a': 1})

            '''
            if not isinstance(other, Counter):
                return NotImplemented
            _max = max
            result = Counter()
            for elem in set(self) | set(other):
                newcount = _max(self[elem], other[elem])
                if newcount > 0:
                    result[elem] = newcount
            return result

        def __and__(self, other):
            ''' Intersection is the minimum of corresponding counts.

            >>> Counter('abbb') & Counter('bcc')
            Counter({'b': 1})

            '''
            if not isinstance(other, Counter):
                return NotImplemented
            _min = min
            result = Counter()
            if len(self) < len(other):
                self, other = other, self
            for elem in ifilter(self.__contains__, other):
                newcount = _min(self[elem], other[elem])
                if newcount > 0:
                    result[elem] = newcount
            return result


if __name__ == '__main__':
    import doctest
    print(doctest.testmod())
