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If your input contains negative numbers, you can use an offset to map them to positive indices
vector<int> computeFrequencyWithOffset(const vector<int>& arr) {
int min_val = *min_element(arr.begin(), arr.end());
int max_val = *max_element(arr.begin(), arr.end());
int offset = -min_val;
vector<int> freq(max_val - min_val + 1, 0);
for (int num : arr) freq[num + offset]++;
return freq;
}