R · version 4

Run R 4 online

R 4 — run it in a Firecracker microVM on ls-judge. Real toolchain, no wrapper.

Starter code

What you get in R 4

Clicking "Run now" opens the playground with this exact code and a matching test case — passes on first Run.

r
R 4
n <- as.integer(scan("stdin", integer(), n=1, quiet=TRUE))
cat(n * 2, "\n", sep="")
stdin →21
expected →42
How it runs

How ls-judge runs R 4

Every submission is compiled and executed inside its own Firecracker microVM — the same isolation primitive AWS Lambda uses. No shared container, no shared kernel with other users' code. The R 4toolchain shipped with the microVM is the real thing (not a browser-side emulation): syscalls behave the way they do in production, and the compile / runtime behaviour matches what you would see on your own machine with that version installed.

Feed stdin from the Tests panel, watch verdicts stream per test case over a WebSocket. Free to use, no sign-up, works from any browser.