cheatLinefunction

CHEAT: one unfinished line drawn for the player, correctly. John, 2026-09-26: beyond Check, which only flashes the unjoined pairs, "a Cheat button that draws one unfinished line correctly", offered only where "Allow cheating" was chosen at set-up. Flow Free's hint does the same — it draws one whole flow.

The line is the lowest-numbered pair not yet joined; where every pair is joined but the board is wrong, the lowest whose line is not the answer's. It is drawn as the answer has it, and any other line in its way is cut back to before the first cell it would share — on a bridge only where both go the same way over it, since two lines may cross there. Null when there is nothing to draw: every line already the answer's. Pure: new lines, the old untouched.

import { cheatLine } from "@johnmorrisdotca/tsunagi";

function cheatLine(layout: LinkLayout, lines: Lines, answer: Lines): { lines: Lines; pair: number; } | null

import { TSUNAGI_4 } from "@johnmorrisdotca/tsunagi/levels-4";
import { cheatLine, decodeLayout, linesOfAnswer, noLines } from "@johnmorrisdotca/tsunagi";

const givens = TSUNAGI_4[0][0];
const answer = TSUNAGI_4[0][1];
const layout = decodeLayout(givens,4)!;
const lines = noLines(layout);
const solvedLines = linesOfAnswer(layout,answer)!;
console.log(cheatLine(layout,lines,solvedLines));

{ lines: [ [ 0, 1, 2, 3 ], [], [], [] ], pair: 0 }