70 lines
2.2 KiB
JavaScript
70 lines
2.2 KiB
JavaScript
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const fs = require('fs');
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const data = fs.readFileSync('input.txt', 'utf-8');
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const lines = data.split('\n').map(num => parseInt(num)).sort((a,b)=>(a-b));
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lines.unshift(0);
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lines.push(lines[lines.length-1]+3);
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// convert to linked list
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let last = {};
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let i = 0
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do {
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let entry = {
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value: lines[i],
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prev: last
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};
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last.next = entry;
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last = entry;
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i++;
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} while (i < lines.length)
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// find removeable adaptors
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let removeableAdaptors = [];
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const lastVal = last
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last = last.prev
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while (last.prev) {
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if (last.next.value - last.prev.value <= 3){
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removeableAdaptors.push(last)
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}
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last = last.prev
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}
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// divide removeable adaptors into groups that don't interfere with one another when removed
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// this changes the runtime with the given input from a over a month to less than a millisecond
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// however, in a worst case scenareo, where every adaptor is removeable, this would still take trillions of years.
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let adaptorGroups = []
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function makeGroups(removeableAdaptors) {
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for (let i = removeableAdaptors.length-1; i>-1; i--) {
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// if the gap between two removeable adaptors > 2 then you know they will not intefere with each other
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if (i == 0 || removeableAdaptors[i-1].value - removeableAdaptors[i].value > 2) {
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adaptorGroups.push(removeableAdaptors.slice(i))
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makeGroups(removeableAdaptors.slice(0, i))
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break;
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}
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}
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}
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makeGroups(removeableAdaptors)
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function findArrangements (removeableAdaptors, s = 0) {
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total = 1
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// for each adaptor in the group
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for (let i = s; i < removeableAdaptors.length; i++){
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// if you can remove this adaptor
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if (removeableAdaptors[i].next.value-removeableAdaptors[i].prev.value <= 3) {
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// remove the adaptor and find arrangements with it gone
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removeableAdaptors[i].prev.next = removeableAdaptors[i].next
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total += findArrangements (removeableAdaptors, i+1)
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// add the adaptor back for following tests
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removeableAdaptors[i].prev.next = removeableAdaptors[i]
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}
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}
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return total
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}
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console.time('time')
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// multipy the amount of arrangements in each group to get the total amount of arrangements.
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answer = adaptorGroups.reduce((a, g) => {return a*findArrangements(g)},1)
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console.timeEnd('time')
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console.log(answer)
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