JavaScript/Search/InterpolationSearch.js

/**
 * Interpolation Search
 *
 * Time Complexity:
 * -Best case: O(1)
 * -Worst case: O(n)
 * -O((log(log(n))) If the data are uniformly distributed
 *
 *
 */

export function interpolationSearch (arr, key) {
  const length = arr.length - 1
  let low = 0
  let high = length
  let position = -1
  let delta = -1

  // Because the array is sorted the key must be between low and high
  while (low <= high && key >= arr[low] && key <= arr[high]) {
    delta = (key - arr[low]) / (arr[high] - arr[low])
    position = low + Math.floor((high - low) * delta)

    // Target found return its position
    if (arr[position] === key) {
      return position
    }

    // If the key is larger then it is in the upper part of the array
    if (arr[position] < key) {
      low = position + 1
      // If the key is smaller then it is in the lower part of the array
    } else {
      high = position - 1
    }
  }

  return -1
}

// const arr = [2, 6, 8, 10, 12, 14, 16, 18, 20, 22, 26, 34, 39]

// interpolationSearch(arr, 2)
// interpolationSearch(arr, 12)
// interpolationSearch(arr, 1000)
// interpolationSearch(arr, 39)