@bazilio-san/af-stream/src/utils/find-index-of-nearest-smaller-in-num-array.ts

Data stream from database table

export const findIndexOfNearestSmallerInNumArrayLEFT = (arr: number[], x: number) => {
  if (!arr.length) {
    return -1;
  }
  const index = arr.findIndex((v) => v >= x);
  if (index > -1) {
    return index - 1;
  }
  if (x < arr[0]) {
    return -1;
  }
  return arr.length - 1;
};

export const findIndexOfNearestSmallerInNumArrayRIGHT = (arr: number[], x: number) => {
  let pos = arr.length;
  if (pos) {
    while (--pos >= 0) {
      if (arr[pos] < x) {
        return pos;
      }
    }
  }
  return -1;
};

export const findIndexOfNearestSmallerInNumArrayBINARY = (arr: number[], x: number) => {
  let start = 0;
  let end = arr.length - 1;
  let ans = -1;
  while (start <= end) {
    const mid = Math.floor((start + end) / 2);
    if (arr[mid] === x) {
      return mid - 1;
    }
    if (arr[mid] > x) {
      end = mid - 1;
    } else {
      ans = mid;
      start = mid + 1;
    }
  }
  return ans;
};

export const findIndexOfNearestSmallerInNumArray = (arr: number[], x: number) => {
  const { length } = arr;
  if (!length) {
    return -1;
  }
  if (length > 2000) {
    return findIndexOfNearestSmallerInNumArrayBINARY(arr, x);
  }
  return ((arr[length - 1] - arr[0]) / 2) < x
    ? findIndexOfNearestSmallerInNumArrayRIGHT(arr, x)
    : findIndexOfNearestSmallerInNumArrayLEFT(arr, x);
};