Given a sorted array of numbers, return the summary of its ranges.

## Examples
```python
summary_ranges([1, 2, 3, 4]) == ["1->4"]
summary_ranges([1, 1, 1, 1, 1]) == ["1"]
summary_ranges([0, 1, 2, 5, 6, 9]) == ["0->2", "5->6", "9"]
summary_ranges([0, 1, 2, 3, 3, 3, 4, 5, 6, 7]) == ["0->7"]
summary_ranges([0, 1, 2, 3, 3, 3, 4, 4, 5, 6, 7, 7, 9, 9, 10]) == ["0->7", "9->10"]
summary_ranges([-2, 0, 1, 2, 3, 3, 3, 4, 4, 5, 6, 7, 7, 9, 9, 10, 12]) == ["-2", "0->7", "9->10", "12"]
```

Difficulty: EASY
Starter code: def summary_ranges(nums):
	

Solutions:
def summary_ranges(nums):
	(ret, s) = ([], float('-inf'))
	for (e, n) in zip([s] + nums, nums + [-s]):
		if n - e > 1:
			ret.append(['{}', '{}->{}'][s < e].format(s, e))
			s = n
	return ret[1:]


def summary_ranges(nums):
	if not nums:
		return []
	ranges = []
	first = nums[0]
	for (current, previous) in zip(nums[1:], nums[:-1]):
		if current - previous not in [0, 1]:
			ranges.append((first, previous))
			first = current
	ranges.append((first, nums[-1]))
	return ['{}->{}'.format(a, b) if a != b else str(a) for (a, b) in ranges]


def summary_ranges(nums):
	nums.append(float('inf'))
	(i, result) = (nums[0], [])
	for (j, n) in zip(nums, nums[1:]):
		if n - j > 1:
			result.append(str(i) if i == j else f'{i}->{j}')
			i = n
	return result


def summary_ranges(nums):
	(result, start) = ([], float('-inf'))
	for (a, b) in zip([start] + nums, nums + [-start]):
		if b - a > 1:
			result.append((start, a))
			start = b
	return [[f'{a}', f'{a}->{b}'][b > a] for (a, b) in result[1:]]


def summary_ranges(nums):
	(l, index) = ([[]], 0)
	for x in nums:
		if not l[index] or l[index][-1] + 1 == x:
			l[index].append(x)
		elif l[index] != [x]:
			l.append([x])
			index += 1
	return [] if not nums else [str(x[0]) if len(x) < 2 else f'{x[0]}->{x[-1]}' for x in l]


def summary_ranges(nums):

	def f():
		cur = []
		for x in nums:
			if not cur:
				cur = [x]
			elif x == cur[-1] + 1:
				cur[1:] = (x,)
			elif x != cur[-1]:
				yield cur
				cur = [x]
		if cur:
			yield cur
	return [str(xs[0]) if xs[0] == xs[-1] else f'{xs[0]}->{xs[-1]}' for xs in f()]


def summary_ranges(nums):
	if not nums:
		return []
	(r, s, l) = ([], nums[0], nums[0])
	for n in nums:
		if n - l > 1:
			r.append(str(s) + '->' + str(l) if s != l else str(s))
			s = n
		l = n
	r.append(str(s) + '->' + str(l) if s != l else str(s))
	return r


def summary_ranges(a):
	(a, i, li) = (sorted(set(a), key=a.index), 0, [])
	while i < len(a):
		temp = [a[i]]
		i += 1
		while i < len(a) and temp[-1] + 1 == a[i]:
			temp.append(a[i])
			i += 1
		li.append(temp)
	return [f'{i[0]}->{i[-1]}' if len(i) > 1 else f'{i[0]}' for i in li]


def summary_ranges(nums):
	(i, lst, nums) = (0, [], sorted(set(nums)))
	while i < len(nums):
		(i, j) = (i + 1, i)
		while i < len(nums) and nums[i] == nums[i - 1] + 1:
			i += 1
		lst.append(str(nums[j]) if j + 1 == i else '{}->{}'.format(nums[j], nums[i - 1]))
	return lst