README_EN.md

2090. K Radius Subarray Averages

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Description

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.

 

Example 1:

Input: nums = [7,4,3,9,1,8,5,2,6], k = 3
Output: [-1,-1,-1,5,4,4,-1,-1,-1]
Explanation:
- avg[0], avg[1], and avg[2] are -1 because there are less than k elements before each index.
- The sum of the subarray centered at index 3 with radius 3 is: 7 + 4 + 3 + 9 + 1 + 8 + 5 = 37.
  Using integer division, avg[3] = 37 / 7 = 5.
- For the subarray centered at index 4, avg[4] = (4 + 3 + 9 + 1 + 8 + 5 + 2) / 7 = 4.
- For the subarray centered at index 5, avg[5] = (3 + 9 + 1 + 8 + 5 + 2 + 6) / 7 = 4.
- avg[6], avg[7], and avg[8] are -1 because there are less than k elements after each index.

Example 2:

Input: nums = [100000], k = 0
Output: [100000]
Explanation:
- The sum of the subarray centered at index 0 with radius 0 is: 100000.
  avg[0] = 100000 / 1 = 100000.

Example 3:

Input: nums = [8], k = 100000
Output: [-1]
Explanation: 
- avg[0] is -1 because there are less than k elements before and after index 0.

 

Constraints:

• n == nums.length
• 1 <= n <= 105
• 0 <= nums[i], k <= 105

Solutions

Python3

class Solution:
    def getAverages(self, nums: List[int], k: int) -> List[int]:
        n = len(nums)
        presum = [0] * (n + 1)
        for i in range(n):
            presum[i + 1] = presum[i] + nums[i]
        return [-1 if i - k < 0 or i + k >= n else (presum[i + k + 1] - presum[i - k]) // (k * 2 + 1) for i in range(n)]

Java

class Solution {
    public int[] getAverages(int[] nums, int k) {
        int n = nums.length;
        long[] presum = new long[n + 1];
        for (int i = 0; i < n; ++i) {
            presum[i + 1] = presum[i] + nums[i];
        }
        int[] ans = new int[n];
        for (int i = 0; i < n; ++i) {
            if (i - k < 0 || i + k >= n) {
                ans[i] = -1;
            } else {
                ans[i] = (int) ((presum[i + k + 1] - presum[i - k]) / (k * 2 + 1));
            }
        }
        return ans;
    }
}

*TypeScipt

function getAverages(nums: number[], k: number): number[] {
    const n = nums.length;
    const l = 2 * k + 1;
    let sum = 0;
    let ans = new Array(n).fill(-1);
    for (let i = 0; i < n; i++) {
        sum += nums[i];
        let shiftIndex = i - l;
        if (shiftIndex > -1) {
            sum -= nums[shiftIndex];
        }
        if (i + 1 >= l) {
            ans[i - k] = Math.floor(sum / l);
        }
    }
    return ans;
}

C++

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

Go

func getAverages(nums []int, k int) []int {
	n := len(nums)
	presum := make([]int64, n+1)
	for i, num := range nums {
		presum[i+1] = presum[i] + int64(num)
	}
	var ans []int
	for i := 0; i < n; i++ {
		if i-k < 0 || i+k >= n {
			ans = append(ans, -1)
		} else {
			ans = append(ans, int((presum[i+k+1]-presum[i-k])/int64(k*2+1)))
		}
	}
	return ans
}

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