Implement `String#parse_mana_cost`, which parses [Magic: the Gathering mana costs](http://mtgsalvation.gamepedia.com/Mana_cost) expressed as a string and returns a `Hash` with keys being kinds of mana, and values being the numbers.

Don't include any mana types equal to zero.

Format is:

* optionally natural number representing total amount of generic mana (use key `*`)
* optionally followed by any combination of `w`, `u`, `b`, `r`, `g` (case insensitive in input, return lower case in output), each representing one mana of specific color.

If case of Strings not following specified format, return `nil/null/None`.

Difficulty: EASY
Starter code: def parse_mana_cost(mana):
	

Solutions:
import re

def parse_mana_cost(mana):
	n = {c: mana.lower().count(c) for c in 'wubrg' if mana.lower().count(c) > 0}
	m = re.split('\\D', mana)
	if sum(n.values()) + sum([len(c) for c in m]) != len(mana):
		return None
	p = sum([int(c) for c in m if c != ''])
	if p > 0:
		n['*'] = p
	return n


import re

def parse_mana_cost(mana):
	m = re.match('(\\d*)([wubrg]*)\\Z', mana.lower())
	if m is None:
		return
	(g, c) = m.groups()
	result = {} if g in ('', '0') else {'*': int(g)}
	result.update({k: c.count(k) for k in set(c)})
	return result


from collections import Counter

def parse_mana_cost(mana):
	if mana != mana.strip() or [c for c in mana.lower() if c not in '0123456789 wubrg']:
		return None
	return Counter(''.join((parse(w) for w in mana.lower().split())))

def parse(w):
	s = '0'
	while w and w[0].isdigit():
		(s, w) = (s + w[0], w[1:])
	return w + '*' * int(s)


import re

def parse_mana_cost(mana):
	retval = {}
	mana = mana.lower()
	m = re.match('\\A(\\d*)([wubrg]*)\\Z', mana)
	if m:
		if m.group(1) and int(m.group(1)) > 0:
			retval['*'] = int(m.group(1))
		if m.group(2):
			l = list(m.group(2))
			print(l)
			if l.count('w') > 0:
				retval['w'] = l.count('w')
			if l.count('u') > 0:
				retval['u'] = l.count('u')
			if l.count('b') > 0:
				retval['b'] = l.count('b')
			if l.count('r') > 0:
				retval['r'] = l.count('r')
			if l.count('g') > 0:
				retval['g'] = l.count('g')
		return retval


import re
from collections import Counter

def parse_mana_cost(mana):
	for (cnt, chrs) in re.findall('\\A(\\d*)([wubrg]*)\\Z', mana.lower() or '0'):
		result = {'*': int(cnt or 0), **Counter(chrs)}
		return {key: result[key] for key in result if result[key]}


from collections import Counter
import re

def parse_mana_cost(s):
	s = s.lower()
	if re.match('\\d*[wubrg]*\\Z', s):
		r = {x: s.count(x) for x in set(s) if x.isalpha()}
		return s and s[0].isdigit() and int(s[0]) and r.update({'*': int(re.match('\\d+', s).group())}) or r


import re

def parse_mana_cost(m):
	if not m:
		return {}
	if not re.match('^[\\dwubrg]+$', m, re.I) or '\n' in m:
		return
	(r1, r) = (re.findall('[wubrg]', m, re.I), re.search('^[0-9]*', m))
	(r, d) = (r.group() if r else '', {})
	if r != '0' and r:
		d['*'] = int(r)
	for i in m[len(r):]:
		d[i.lower()] = d.get(i.lower(), 0) + 1
	return d


import re

def parse_mana_cost(mana):
	mana = mana.lower()
	valid = ['w', 'u', 'r', 'g', 'b']
	dic = {}
	regex = re.compile('(\\d*)([wubrg]*)')
	match = regex.search(mana)
	for x in list(mana):
		if x in valid:
			dic[x] = dic[x] + 1 if x in dic else 1
	if match.group(1) and match.group(1) != '0':
		dic['*'] = int(match.group(1))
	return dic if ''.join(match.group()) == mana else None


from itertools import groupby
import re

def parse_mana_cost(mana):
	result = {}
	pattern = re.compile('\\d*[wurbg]*', re.I)
	manacost = pattern.match(mana).group()
	if mana in ['', '0']:
		return {}
	if manacost == None or len(mana) != len(manacost):
		return None
	(colors, colorless) = ('', '')
	for i in manacost:
		if i.isalpha():
			colors += i
		else:
			colorless += i
	if colorless not in ['0', '']:
		result['*'] = int(colorless)
	colors = ''.join(sorted(list(colors)))
	for (key, count) in groupby(colors):
		result[key.lower()] = len(list(count))
	return result