2b.js

import {readInput} from "./lib.js";
import * as assert from "node:assert";

const input = readInput(2)

assert.ok(!isSafe('1 2 1'.split(' '))); // up then down
assert.ok(!isSafe('1 2 2'.split(' '))); // no inc
assert.ok(!isSafe('1 2 10'.split(' '))); // big inc

assert.ok(!isSafe('1 2 1'.split(' '))); // down then up
assert.ok(!isSafe('2 1 1'.split(' '))); // no dec
assert.ok(!isSafe('10 9 1'.split(' '))); // big inc

assert.ok(!isSafe('14 13 14 12 15 18 15'.split(' '))); // down up down

const answer = input
    .map((line) => {
        return line.split(' ').map((x) => parseInt(x));
    })
    .filter((report) => {
        if (isSafe(report)) {
            return true;
        }

        for (let i = 0; i < report.length; i++) {
            const left = report.slice(0, i);
            const right = report.slice(i + 1);

            if (isSafe([...left, ...right])) {
                return true;
            }
        }

        return false;
    })
    .length;

function isSafe(report) {
    const [first, second] = report;
    const up = first < second;

    for (let i = 1; i < report.length; i++) {
        const lvl = report[i];
        const prevLvl = report[i - 1];
        let difference = lvl - prevLvl;

        difference = up ? difference : -difference;

        if (difference > 3 || difference <= 0) {
            return false;
        }
    }

    return true;
}

console.log(answer);