Given a non-empty array of non-negative integers nums
, the degree of this array is defined as the maximum frequency of any one of its elements.
Your task is to find the smallest possible length of a (contiguous) subarray of nums
, that has the same degree as nums
.
Example 1:
Input: [1, 2, 2, 3, 1]
Output: 2
Explanation:
The input array has a degree of 2 because both elements 1 and 2 appear twice.
Of the subarrays that have the same degree:
[1, 2, 2, 3, 1], [1, 2, 2, 3], [2, 2, 3, 1], [1, 2, 2], [2, 2, 3], [2, 2]
The shortest length is 2. So return 2.
Example 2:
Input: [1,2,2,3,1,4,2]
Output: 6
Note:
nums.length
will be between 1 and 50,000.
nums[i]
will be an integer between 0 and 49,999.
class Solution(object):
def findShortestSubArray(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
# use pos_map to record num's start pos and end pos in nums
pos_map = {}
for i,n in enumerate(nums):
if n not in pos_map:
pos_map[n] = [i, i]
else:
pos_map[n][1] = i
# find max_freq number (maybe have many)
cnt = collections.Counter(nums)
max_freq = 0
max_freq_num = []
for k,v in cnt.iteritems():
if v > max_freq:
max_freq = v
max_freq_num = [k]
elif v == max_freq:
max_freq_num.append(k)
# find min degree
return min(pos_map[n][1]-pos_map[n][0]+1 for n in max_freq_num)
精简代码:
class Solution:
def findShortestSubArray(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
pos_map = {}
for i,n in enumerate(nums):
if n not in pos_map:
pos_map[n] = [i, i]
else:
pos_map[n][1] = i
cnt = collections.Counter(nums)
max_freq_num = max(cnt.values())
return min(pos_map[n][1]-pos_map[n][0]+1 for n in cnt if cnt[n] == max_freq_num)
更精简的:
class Solution:
def findShortestSubArray(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
c = collections.Counter(nums)
first, last = {}, {}
for i, v in enumerate(nums):
first.setdefault(v, i)
last[v] = i
degree = max(c.values())
return min(last[v] - first[v] + 1 for v in c if c[v] == degree)
注意:
Python 字典(Dictionary) setdefault()方法
描述
Python 字典 setdefault() 函数和get() 方法类似, 如果键不存在于字典中,将会添加键并将值设为默认值。
语法
setdefault()方法语法:
dict.setdefault(key, default=None)
参数
- key -- 查找的键值。
- default -- 键不存在时,设置的默认键值。
返回值
如果字典中包含有给定键,则返回该键对应的值,否则返回为该键设置的值。
实例
以下实例展示了 setdefault() 函数的使用方法:
以上实例输出结果为:
Value : 菜鸟教程
Value : 淘宝