228 summary ranges
228. Summary Ranges
题目: https://leetcode.com/problems/summary-ranges/
难度:
Medium
Just collect the ranges, then format and return them.
class Solution(object):
def summaryRanges(self, nums):
"""
:type nums: List[int]
:rtype: List[str]
"""
ranges = []
for i in nums:
if not ranges or i > ranges[-1][-1] + 1:
ranges += [],
ranges[-1][1:] = i,
return ['->'.join(map(str, r)) for r in ranges]
About the commas :-)
ranges += [],
r[1:] = n,
Why the trailing commas? Because it turns the right hand side into a tuple and I get the same effects as these more common alternatives:
ranges += [[]]
or
ranges.append([])
r[1:] = [n]
Without the comma, …
- ranges += [] wouldn’t add [] itself but only its elements, i.e., nothing.
- r[1:] = n wouldn’t work, because my n is not an iterable.
Why do it this way instead of the more common alternatives I showed above? Because it’s shorter and faster (according to tests I did a while back).
写到这里可能又有疑问了🤔️，为什么不可以直接写ranges[-1][1] = i呢，当然是会报IndexError: list assignment index out of range错误啦，那为什么ranges[-1][1:] = i,可以呢？
简单来说
L1=L 与 L1=L[:] - L1和L 都是对同一个对象的引用（所谓绑定的意思）。 - L[:] 是生成了一个和L不同的新的对象，L1 变为了L[:] 这个对象的引用。
参考stefan
