The Sealed Vault of Hollowmere

By commission of the Wardens' Guild of Bitwick.

Beneath the ruined keep of Hollowmere lies a vault sealed by a rune lock. The door answers to one fixed sequence of runes, its *code*, pressed one rune at a time. The Guild has recovered the code and the exact runes a failed expedition pressed. It pays for a faithful reckoning of every moment the door stood open.

Write runeLock(code, presses).

• code is a non-empty string of uppercase letters. Each letter is one rune.
• presses is a string of uppercase letters, possibly empty. These are the runes pressed, in order.

The lock tracks four whole numbers, all starting at 0: progress, strikes, silence and lockouts.

Handle the presses in order. For the press at 0-based index i with rune r:

1. If silence is greater than 0, reduce silence by 1. The press has no other effect. 2. Otherwise, if `r` equals the rune at 0-based position progress in `code`, increase progress by 1. If progress now equals the length of code, the door opens at index i. Record i, then set progress to 0 and strikes to 0. 3. Otherwise the press is a strike. Increase strikes by 1. - If strikes is now 3, the lock seals itself. Increase lockouts by 1, set silence equal to the new value of lockouts, and set strikes to 0 and progress to 0. - If strikes is not 3, set progress to 1 if r equals the first rune of code, and to 0 otherwise.

A correct press never changes strikes. Only an opening or a lockout clears it. Lockouts is never reset.

Return a list of every index at which the door opened, in increasing order. Return an empty list if it never opened.