Sliding Window: find averages of subarrays

findAveragesOfSubarrays.js

function find_averages_of_subarrays(K, arr) {
  const result = []
  let windowSum = 0
  let windowStart = 0
  
  for (let windowEnd = 0; windowEnd < arr.length; windowEnd++) {
    // Push the last element back, slide new element as the last one
    windowSum += arr[windowEnd]
    
    // We reached a window with 5 elements
    if (windowEnd >= K - 1) {
      result.push(windowSum / 5)
      
      // Slide the first element out
      windowSum -= arr[windowStart]
      // Replace the first element with the second one
      windowStart += 1
    }
  }
  
  return result
}


const result = find_averages_of_subarrays(5, [1, 3, 2, 6, -1, 4, 1, 8, 2]);
console.log(`Averages of subarrays of size K: ${result}`);

/*
K = 5
K - 1 = 4
windowStart = 0
// i = 0
WindowSum = 1

// i = 1
windowSum = 1 + 3

// i = 2
windowSum = 1 + 3 + 2

// i = 3
windowSum = 1 + 3 + 2 + 6

// i = 4
windowSum = 1 + 3 + 2 + 6 + -1
windowSum -= arr[windowStart]
windowStart += 1
windowSum = 3 + 2 + 6 + -1

// i = 5
windowSum = 3 + 2 + 6 + -1 + 4
windowSum -= arr[windowStart]
windowStart += 1
windowSum = 2 + 6 + -1 + 4

// i = 6
windowSum = 2 + 6 + -1 + 4 + 1
windowSum -= arr[windowStart]
windowStart += 1
windowSum = 6 + -1 + 4 + 1

// i = 7
windowSum = 6 + -1 + 4 + 1 + 8
windowSum -= arr[windowStart]
windowStart += 1
windowSum = -1 + 4 + 1 + 8

// i = 7
windowSum = -1 + 4 + 1 + 8 + 2
windowSum -= arr[windowStart]
windowStart += 1
windowSum = 4 + 1 + 8 + 2

*/