Given an unsorted array of integers which may contain repeated elements, sort the elements in descending order of some of its occurrence. If there exists more than one element whose sum of occurrences are the same then, the one which is greater will come first.

**Examples:**

Input:arr[] = [2, 4, 1, 2, 4, 2, 10]

Output:arr[] = [10, 4, 4, 2, 2, 2, 1]

Explanation:

Here, 2 appears 3 times, 4 appears 2 times, 1 appears 1 time and 10 appears 1 time.

Thus,

Sum of all occurrences of 2 in given array = 2 * 3 = 6,

Sum of all occurrences of 4 = 4 * 2 = 8,

Sum of all occurrences of 10 = 10 * 1 = 10,

Sum of all occurrences of 1 = 1 * 1 = 1.

Therefore sorting the array in descending order based on the above sum = [ 10, 4, 4, 2, 2, 2, 1 ]

Input2:arr[] = [2, 3, 2, 3, 2, 1, 1, 9, 6, 9, 1, 2]

Output2:[9, 9, 2, 2, 2, 2, 6, 3, 3, 1, 1, 1]

**Approach:**

- Create a map that will map elements to it appearence ie if a occur one time then a will map to a but if a occur m times then a will be map to a*m.
- After doing the mapping sort the dictionary in descending order based on their values not keys. In case of tie, sort based on values.
- Finaly copy the sorted dictionary keys in final output array and there frequency is obtain based on their key-value pairs i.e. if a is mapped to a*m it means we need to include a, m times in output array.

Below is the implementation of the above approach:

## Python

`# Python3 program to sort elements of ` `# arr[] in descending order of sum ` `# of its occurrence ` ` ` `def` `sort_desc(arr): ` ` ` ` ` `# to store sum of all ` ` ` `# occurrences of an elements ` ` ` `d_sum ` `=` `{} ` ` ` ` ` `# to store count of ` ` ` `# occurrence of elements ` ` ` `d_count ` `=` `{} ` ` ` ` ` `# to store final result ` ` ` `ans ` `=` `[] ` ` ` ` ` `# to store maximum sum of occurrence ` ` ` `mx ` `=` `0` ` ` ` ` `# Traverse and calculate sum ` ` ` `# of occurrence and count of ` ` ` `# occurrence of elements of arr[] ` ` ` `for` `x ` `in` `arr: ` ` ` `if` `x ` `not` `in` `d_sum: ` ` ` `d_sum[x] ` `=` `x ` ` ` `d_count[x] ` `=` `1` ` ` `else` `: ` ` ` `d_sum[x] ` `+` `=` `x ` ` ` `d_count[x] ` `+` `=` `1` ` ` ` ` `# sort d_sum in decreasing order of its value ` ` ` `l ` `=` `sorted` `(d_sum.items(), ` ` ` `reverse ` `=` `True` `, ` ` ` `key ` `=` `lambda` `x:(x[` `1` `], x[` `0` `])) ` ` ` ` ` `# store the final result ` ` ` `for` `x ` `in` `l: ` ` ` `ans ` `+` `=` `[x[` `0` `]] ` `*` `d_count[x[` `0` `]] ` ` ` ` ` `return` `ans ` ` ` `# Driver Code ` `arr ` `=` `[` `3` `, ` `5` `, ` `2` `, ` `2` `, ` `3` `, ` `1` `, ` `3` `, ` `1` `] ` `print` `(sort_desc(arr)) ` |

*chevron_right*

*filter_none*

**Output:**

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

**Time Complexity: **O(N*log N).

**Space Complexity: **O(N).

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready.

## Recommended Posts:

- Sort prime numbers of an array in descending order
- Sort an array of strings based on the given order
- Stable sort for descending order
- Program to sort string in descending order
- Sorting Vector of Pairs in C++ | Set 2 (Sort in descending order by first and second)
- Sort all even numbers in ascending order and then sort all odd numbers in descending order
- Sort Matrix in alternating ascending and descending order rowwise
- Sort first k values in ascending order and remaining n-k values in descending order
- Sort first half in ascending and second half in descending order | 1
- Sort first half in ascending and second half in descending order | Set 2
- Rearrange array such that difference of adjacent elements is in descending order
- Print the last occurrence of elements in array in relative order
- Sorting rows of matrix in descending order followed by columns in ascending order
- Sorting rows of matrix in ascending order followed by columns in descending order
- Sort the character array based on ASCII % N
- Sort an array of strings lexicographically based on prefix
- Sort an array of strings based on the frequency of good words in them
- Sort an Array based on the absolute difference of adjacent elements
- Sort an array of strings based on count of distinct characters
- Sort an array where a subarray of a sorted array is in reverse order

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.