2090. K Radius Subarray Averages

You are given a 0-indexed array nums of n integers, and an integer k.

The k-radius average for a subarray of nums centered at some index i with the radius k is the average of all elements in nums between the indices i - k and i + k (inclusive). If there are less than k elements before or after the index i, then the k-radius average is -1.

Build and return an array avgs of length n where avgs[i] is the k-radius average for the subarray centered at index i.

The average of x elements is the sum of the x elements divided by x, using integer division. The integer division truncates toward zero, which means losing its fractional part.

• For example, the average of four elements 2, 3, 1, and 5 is (2 + 3 + 1 + 5) / 4 = 11 / 4 = 2.75, which truncates to 2.

class Solution {
public:
    vector<int> getAverages(vector<int>& nums, int k) {
        vector<int> res(nums.size(), -1);
        long long det = 2 * k + 1;
        if(det > nums.size()) return res;
        long long prefixSum = accumulate(nums.begin(), nums.begin() + det, 0ll);
        res[k] = prefixSum / det;
        for(int i = det; i < nums.size(); i++) {
            prefixSum += nums[i] - nums[i-det];
            res[i-k] = prefixSum / det;
        }
        return res;
    }
};