K radius subarray averages

Array Sliding Window

46.1% acceptance

Feb 25, 2026

2087

104

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.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn get_averages(nums: Vec<i32>, k: i32) -> Vec<i32> {
    let n = nums.len();
    let k = k as usize;
    let window = 2 * k + 1;
    let mut avgs = vec![-1i32; n];
    if window > n {
      return avgs;
    }
    // Prefix sum
    let mut prefix = vec![0i64; n + 1];
    for i in 0..n {
      prefix[i + 1] = prefix[i] + nums[i] as i64;
    }
    for i in k..n - k {
      let sum = prefix[i + k + 1] - prefix[i - k];
      avgs[i] = (sum / window as i64) as i32;
    }
    avgs
  }
}