Encode Keys

You are given a list of string keys. Build: 1) unique: the distinct keys in the order they first appear, and 2) ids: an integer array where ids[i] is the index of keys[i] in unique.

Return both arrays.

Function signature

func EncodeKeys(keys []string) ([]string, []int)

Example

keys   = ["us", "ca", "us", "mx", "ca"]
unique = ["us", "ca", "mx"]
ids    = [0, 1, 0, 2, 1]

Constraints

• 0 <= len(keys) <= 200_000
• 1 <= len(keys[i]) <= 32
• keys contain ASCII letters, digits, or "_"

Notes

• Aim for O(n) time using a hash map.
• Preallocate slices to avoid repeated growth.