70 lines
1.6 KiB
JavaScript
70 lines
1.6 KiB
JavaScript
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const fs = require('fs'); // file system
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const input = fs.readFileSync(`${__dirname}/input.txt`, 'utf-8') // read the input file
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.split('\n'); // split on lines
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// get the initial state from the input
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let state = input[0].slice('initial state: '.length);
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let rules = {};
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// extract all rules from input
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for (const line of input.splice(2)) {
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rules[line.slice(0, 5)] = line.slice(9);
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}
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// to add extra pots as if there were endless pots
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function expand (s) {
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let r = s.replace(/^(\.+)?/, '.....');
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r = r.replace(/(\.+)?$/, '.....');
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return r;
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}
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let zero = 5;
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// add empty pots
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state = expand(state);
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let done = false;
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for (var i = 0; i < 250; i++){
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if (done) {
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var gen = i;
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break;
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}
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// create 'empty' array of '.'s
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const pots = Array(3).join('.').split('');
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state.split('').forEach((_, n) => {
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// get the section to look at of prev gen
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const sect = state.slice(n-2, n+3);
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if (sect.length !== 5) { return }
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// get the value of the matching rule
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let plant = rules[sect];
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if (!plant) { return }
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// replace the value in the next gen
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pots.push(plant);
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});
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// move the '0th pot' marker
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zero -= pots.indexOf('#') - 5;
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// if the pattern is repeating. process is done.
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done = expand(pots.join('')) === state;
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// store the generation with extra pots.
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state = expand(pots.join(''));
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// console.log(Array(20-zero).join(' ')+state); // output with pot 0 aligned
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// console.log(state); // output misaligned
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}
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// calculate the value of last gen
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const result = state.split('').reduce((val, pot, index) => {
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return (Number(val) || 0) + (pot === '#' ? index - zero : 0);
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})
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console.log(result + (50000000000 - gen) * state.match(/#/g).length)
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