Given an unsorted array of n integers which can contains n integers. Count frequency of all elements that are present in array. Examples:
Input : arr[] = [1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 5, 5]
Output : 1 -> 4
2 -> 4
3 -> 2
4 -> 1
5 -> 2
This problem can be solved in many ways, refer Count frequencies of all elements in array link. In Python, we can quickly solve this problem in using Collections module.
Implementation:
Python
# Function to count frequency of each elementimport collections# it returns a dictionary data structure whose# keys are array elements and values are their# corresponding frequencies {1: 4, 2: 4, 3: 2,# 5: 2, 4: 1}def CountFrequency(arr): return collections.Counter(arr)# Driver functionif __name__ == "__main__": arr = [1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 5, 5] freq = CountFrequency(arr) # iterate dictionary named as freq to print # count of each element for (key, value) in freq.items(): print (key, " -> ", value) |
(1, ' -> ', 4) (2, ' -> ', 4) (3, ' -> ', 2) (4, ' -> ', 1) (5, ' -> ', 2)
The time complexity of this function is O(n), where n is the length of the input array.
The auxiliary space required by this function is O(k), where k is the number of unique elements in the input array.
Related Article : Counting the frequencies in a list using dictionary in Python This article is contributed by Shashank Mishra (Gullu).
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