> For the complete documentation index, see [llms.txt](https://gl01.gitbook.io/gfg-editorials/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gl01.gitbook.io/gfg-editorials/2023/11-2023-nov/01-frequencies-of-limited-range-array-elements.md).

# 01. Frequencies of Limited Range Array Elements

The problem can be found at the following link: [Question Link](https://www.geeksforgeeks.org/problems/frequency-of-array-elements-1587115620/1)

![](https://badgen.net/badge/Level/Easy/green)

## My Approach

We can make it simpler by using the modulo operation and performing some mathematical operations on the array. Here's how it works:

* Main objective is to modify an array to count the frequencies of elements.
* I increment values at the indices corresponding to the elements in the original array.
* I use an `offset` to distinguish between the modified values and the original values.
* After processing the array, I restore the original values by dividing them by the `offset`.

## Time and Auxiliary Space Complexity

* **Time Complexity**: `O(N)`, where `N` is the size of the array.
* **Auxiliary Space Complexity**: `O(1)`, as I'm modifying the input array in-place.

## Code (C++)

```cpp
class Solution {
public:
    void frequencyCount(vector<int>& arr, int N, int P) {
        int offset = P + 1;

        for (auto i : arr) {
            int val = (i - 1) % offset;
            if (val < N) {
                arr[val] += offset;
            }
        }
        
        for (int i = 0; i < N; ++i) {
            arr[i] /= offset;
        }
    }
};
```

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