347. Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent

elements.

For example, Given [1,1,1,2,2,3] and k = 2, return [1,2].

Note:

•You may assume k is always valid, 1 ≤ k ≤ number of unique elements.

•Your algorithm’s time complexity must be better than O(n log n),

where n is the array’s size.

给一个数组和K值，递减输出K个数组中出现频率最高的元素

Answer with python:

Solution(object):
def topKFrequent(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: List[int]
"""
new_dict = {}                  #set a new dic
for item in nums:              #将数组元素设置为字典的key，value初始化为1
if item not in new_dict:
new_dict[item] =1;
else:                      #计算数组内重复元素的个数，设置为字典的值
new_dict[item] +=1;
sorted_dict = sorted(new_dict, key=new_dict.get, reverse=True) #以字典内values的大小顺序排列
return sorted_dict[:k]   #切片取K个值