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# Program to sort array by increasing frequency of elements in Python

Suppose we have an array with some elements where elements may appear multiple times. We have to sort the array such that elements are sorted according to their increase of frequency. So which element appears less number of time will come first and so on.

So, if the input is like nums = [1,5,3,1,3,1,2,5], then the output will be [2, 5, 5, 3, 3, 1, 1, 1]

To solve this, we will follow these steps −

mp := a new map

for each distinct element i from nums, do

x:= number of i present in nums

if x is present in mp, then

insert i at the end of mp[x]

otherwise mp[x] := a list with only one element i

ans:= a new list

for each i in sort the mp based on key, do

for each j in sort the list mp[i] in reverse order, do

insert j, i number of times into ans

return ans

## Example (Python)

Let us see the following implementation to get better understanding −

def solve(nums): mp = {} for i in set(nums): x=nums.count(i) try: mp[x].append(i) except: mp[x]=[i] ans=[] for i in sorted(mp): for j in sorted(mp[i], reverse=True): ans.extend([j]*i) return ans nums = [1,5,3,1,3,1,2,5] print(solve(nums))

## Input

[1,5,3,1,3,1,2,5]

## Output

[2, 5, 5, 3, 3, 1, 1, 1]

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