Solved! Leetcode 2090. K Radius Subarray Averages

source: https://leetcode.com/problems/k-radius-subarray-averages/description/

K Radius Subarray Averages

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

Solution

class Solution {
    public int[] getAverages(int[] nums, int k) {
        int n = k*2+1;

        int[] res = new int[nums.length];
        Arrays.fill(res, -1);
        if(nums.length<n){
            return res;
        }

        long sum = 0;
        //get the sum of first n numbers
        for(int i=0;i<n;i++){
            sum = sum + nums[i];
        }
        int i=k;
        //sliding window
        for(;i+k+1<nums.length;i++){
            res[i] = (int)(sum/n);
            sum = sum - nums[i-k] + nums[i+k+1]; 
        }
        res[i] = (int)(sum/n);

        return res;
    }
}

class Solution {

public int[] getAverages(int[] nums, int k) {

int n = k*2+1;

int[] res = new int[nums.length];

Arrays.fill(res, -1);

if(nums.length<n){

return res;

}

long sum = 0;

//get the sum of first n numbers

for(int i=0;i<n;i++){

sum = sum + nums[i];

}

int i=k;

//sliding window

for(;i+k+1<nums.length;i++){

res[i] = (int)(sum/n);

sum = sum - nums[i-k] + nums[i+k+1];

}