dichotomid

dichotomid

Dichotomid helps you find the first free id of something, efficiently.

Imagine you have a directory with files named file1, file2, file3, ... and you want to find the first free fileN:

// 🐌 Naive implementation, do not do this 🐌
let i = 1;
while (fs.existsSync(`file${i}`)) {
  i++;
}
console.log(`file${i} is the first free`);

This implementation works, but can be mathematically optimized, and that's what dichotomid is for:

// 🐎 Optimized implementation 🐎
import { dichotomid } from "dichotomid";
let i = dichotomid((i) => fs.existsSync(`file${i}`));
console.log(`file${i} is the first free`);

Dichotomid relies on binary search to find the first free id in the least amount of tests. Indeed, if file1 to file999 are all taken, it would take 1000 existsSync calls to figure it out naively. Dichotomid will find the value in 30 call.

import { dichotomid } from "dichotomid";

let op = 0;
let validator = (n) => {
  op++;
  return n >= 1000; // The first free id is 1000
};

let id = dichotomid(validator);
console.log(op); // 30

Usage

Three functions are made available: dichotomid (default export), dichotomidSync and dichotomidAsync.

dichotomid works for both synchronous and asynchronous validators. It returns a number if the validator is synchronous, or a Promise<number> if the validator is asynchronous.

Notes

• dichotomid has a fail safe if the value offered to the validator exceeds MAX_SAFE_INTEGER.
• The library has 100% test coverage.
• Ids are expected to be contiguous. If they are not, the algorithm you want is the naive loop at the top.