challenge-mockUuid.js

// 
// Coding challenge:
// 
// Write a `mockUuid()` function that each time its called returns
// an incrementing integer formatted as a UUID.
// 
// Then optimize the function to be as fast as you possibly can.
// 

// UUID format:
// XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
// - 32 digits in sections of 8-4-4-4-12
// - each digit is a hexadecimal number (0123456789ABCDEF)
//
// This means every possible UUID can actually be
// represented as a 32-byte (not bit) integer (0 to 32^16).
// 
// 00000000-0000-0000-0000-000000000000 is 0
// 00000000-0000-0000-0000-000000000001 is 1
// ...
// FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFE is 1208925819614629174706175
// FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF is 1208925819614629174706176

let i = 0n // bigint

/** @returns {string} */
function mockUuid() {
  let id = i++
  let hex = id.toString(16)
  // implement me: format as uuid...
}

for (let i = 0; i < 0xFFF) {
  mockUuid() 
}

// "00000000-0000-0000-0000-000000000000" - 0
// "00000000-0000-0000-0000-000000000001" - 1
// ...
// "00000000-0000-0000-0000-00000000000e" - 14
// "00000000-0000-0000-0000-00000000000f" - 15
// "00000000-0000-0000-0000-000000000010" - 16
// "00000000-0000-0000-0000-000000000011" - 17
// ...
// "00000000-0000-0000-0000-0000000000fe" - 254
// "00000000-0000-0000-0000-0000000000ff" - 255
// "00000000-0000-0000-0000-000000000100" - 256
// "00000000-0000-0000-0000-000000000101" - 257
// ...
// "00000000-0000-0000-0000-000000000ffe" - 4094
// "00000000-0000-0000-0000-000000000fff" - 4095

// Say we need to generate a *lot* of UUIDs very very quickly...
// What would be the fastest way of generating all these strings

// Hints:
// - id.toString(16).padStart(32, '0') will give you a UUID without dashes
// - id.slice(0, 8) and id.slice(8, 12) will give you the first two sections of the uuid
// - HOWEVER... we know we always incrementing by 1.
// - AND... most of the time (but not always) only one digit is changing.
// - How could we use this information to produce new strings faster?

// How to measure:
//   Count the total program execution time not just the loop of mockUuid().
//   So precomputing a bunch of values will count toward your total time.