01. Frequencies of Limited Range Array Elements

The problem can be found at the following link: Question Link

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++)

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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