SignalChapter 7: Frames and loops

54RUN LENGTH

The task

X is a stream of frames, each ended by a 0. Within a frame, a run is one value repeated.

For each run, P must receive the value and then how many times it came.

A run always ends where its frame does. e is an SC-4, with two more registers: C and D.

The board

The board as the puzzle screen lays it out. Cyan pins read, lemon pins write, violet pins go both ways. On a narrow screen, scroll the board sideways to see all of it.

Key idea

A run ends at a change or at the frame's 0, and a 0 inside the data is the end, not a value; the coder is an SC-4 that keeps the count in C.

Hints

Each hint goes a step further than the one before. Open them one at a time.

Hint 1Show

Keep the last value in B so you can tell when the next one is different.

Hint 2Show

An SC-4 can keep the count itself: MOV C, A copies A into C, and c can sit idle.

Hint 3Show

A 0 from X is not a run, but it does end the one before it.

Solution

Reveal the Full SolutionThe complete program for RUN LENGTH. Open it only when you want the answer.

The reference program

The game's own solution. It passes every test and scores exactly par on every benchmark.

eSC-4 quad

S: IN P0
SUB B
JZ I
ADD B
XCH A, B
JZ F
OUT P1
MOV A, C
OUT P1
F: MOV A, 1
MOV C, A
JMP S
I: MOV A, C
ADD 1
MOV C, A

CYCLES: 342; at par
ENERGY: 2691; at par
NODES: 1; at par
INSTRUCTIONS: 15; at par

Another way: Two cores

A second program that also passes, by a different road, at a cost on CYCLES, ENERGY, NODES, and INSTRUCTIONS.

The count on c, as before e was an SC-4: correct, but two cores spend more.

eSC-4 quad

S: IN P0
SUB B
JZ T
ADD B
XCH A, B
JZ T
OUT P1
MOV A, 0
OUT P2
IN P3
OUT P1
T: MOV A, B
JZ S
OUT P2

cSC-2 standard

S: IN P0
JZ E
XCH A, B
ADD 1
MOV B, A
JMP S
E: XCH A, B
OUT P1

CYCLES: 446; over par
ENERGY: 4187; over par
NODES: 2; over par
INSTRUCTIONS: 22; over par