2090. K Radius Subarray Averages

Method 1

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.

Method 1

【O(n) time | O(n) space】

package Leetcode.SlideWindow;

import java.util.Arrays;

/**
 * @author zhengxingxing
 * @date 2024/12/22
 */
public class KRadiusSubarrayAverages {

    public static int[] getAverages(int[] nums, int k) {
        int n = nums.length;
        if(n == 0) {
            return new int[0];
        }

        // Initialize result array with -1
        int[] result = new int[n];
        Arrays.fill(result, -1);

        // Running sum of current window
        long windowSum = 0;

        // Window size is 2k + 1
        int windowSize = 2 * k + 1;

        // Iterate through the array
        for(int i = 0; i < n; i++) {
            // Add current element to window sum
            windowSum += nums[i];

            // Skip until we have enough elements (2k+1) in our window
            if(i < windowSize - 1) {
                continue;
            }

            // Calculate average for the current window
            result[i - k] = (int)(windowSum / windowSize);

            // Remove leftmost element from window sum
            // as we'll slide the window right in next iteration
            windowSum -= nums[i - windowSize + 1];
        }
        return result;
    }

    public static void main(String[] args) {
        // Test Case 1: Basic case
        int[] nums1 = {7,4,3,9,1,8,5,2,6};
        int k1 = 3;
        System.out.println("Test Case 1:");
        System.out.println("Input: nums = [7,4,3,9,1,8,5,2,6], k = 3");
        System.out.println("Output: " + Arrays.toString(getAverages(nums1, k1)));
        // Expected output: [-1,-1,-1,5,4,4,4,4,-1]

        // Test Case 2: k = 0
        int[] nums2 = {1,2,3,4,5};
        int k2 = 0;
        System.out.println("\nTest Case 2:");
        System.out.println("Input: nums = [1,2,3,4,5], k = 0");
        System.out.println("Output: " + Arrays.toString(getAverages(nums2, k2)));
        // Expected output: [1,2,3,4,5]

        // Test Case 3: k larger than array size
        int[] nums3 = {1,2,3};
        int k3 = 3;
        System.out.println("\nTest Case 3:");
        System.out.println("Input: nums = [1,2,3], k = 3");
        System.out.println("Output: " + Arrays.toString(getAverages(nums3, k3)));
        // Expected output: [-1,-1,-1]

        // Test Case 4: Empty array
        int[] nums4 = {};
        int k4 = 1;
        System.out.println("\nTest Case 4:");
        System.out.println("Input: nums = [], k = 1");
        System.out.println("Output: " + Arrays.toString(getAverages(nums4, k4)));
        // Expected output: []

        // Test Case 5: Large numbers
        int[] nums5 = {100000,100000,100000,100000};
        int k5 = 1;
        System.out.println("\nTest Case 5:");
        System.out.println("Input: nums = [100000,100000,100000,100000], k = 1");
        System.out.println("Output: " + Arrays.toString(getAverages(nums5, k5)));
        // Expected output: [-1,100000,100000,-1]
    }
}

Method 1

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