66 lines
2 KiB
JavaScript
66 lines
2 KiB
JavaScript
const fs = require('fs');
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const input = fs.readFileSync('input.txt', 'utf-8').split('\n').map(l=>l.split(' = '));
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let mask = [];
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let mem = new Map();
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let memo = new Map()
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let runningTotal = 0
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input.forEach((command,i) => {
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if (command[0] == 'mask') {
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// reset the mask and memorised values from that mask
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mask = command[1].split('');
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memo = new Map();
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} else {
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let value = Number(command[1]);
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let index = Number(command[0].substring(4,command[0].length-1)).toString(2);
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while (index.length < mask.length) {
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index = '0' + index;
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}
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let addresses = [...address(index.split(''))]
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addresses.forEach(add => {
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// keep a running total instead of adding it up at the end by adding the value and subtracting the value that it replaces
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runningTotal += value - (mem.get(parseInt(add, 2))||0)
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mem.set(parseInt(add, 2), value)
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})
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}
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});
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console.log(runningTotal)
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// calculate all addresses from a given address after the mask is applied
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function address(loc, i = 0, found = new Set()) {
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// reached the end of the address
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if (i >= mask.length) {
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// add the new address
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return found.add(loc.join(''))
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}
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// if I have already seen this address ending
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let key = loc.slice(i).join('')
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if (memo.has(key)) {
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// add all the addresses that result from this ending
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let prefix = loc.slice(0,i).join('');
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[...memo.get(key)].forEach(suffix => {found.add(prefix+suffix)});
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return found
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}
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// apply the mask from point i and get all possibilities into the array rem
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let rem = []
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switch (mask[i]) {
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case '1':
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loc[i] = '1'
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case '0':
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rem = [...address([...loc],i+1,found)]
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break;
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case 'X':
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loc[i] = '0';
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rem = [...address([...loc],i+1,found)]
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loc[i] = '1';
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rem.push(...[...address([...loc],i+1,found)])
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break;
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default:
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console.log('oops, bad mask at index', i)
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}
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// store the possibilities in the memo in case we come across this pattern again.
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memo.set(key, new Set(rem.map(o => o.slice(i))))
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return found
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}
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