Created
December 15, 2020 13:35
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| function day15_part2(numbers: number[]) { | |
| const cache = new Array<{ lastSpoken: number; previousSpoken: number }>( | |
| 30000000 | |
| ); | |
| function computeNewNumber(spoken: number) { | |
| const turnSpoken = cache[spoken]; | |
| // first time spoken | |
| if ( | |
| !turnSpoken || | |
| turnSpoken.lastSpoken === -1 || | |
| turnSpoken.previousSpoken === -1 | |
| ) { | |
| return 0; | |
| } | |
| return turnSpoken.lastSpoken - turnSpoken.previousSpoken; | |
| } | |
| numbers.forEach((number, index) => { | |
| cache[number] = { lastSpoken: -1, previousSpoken: index + 1 }; | |
| }); | |
| let newNumber = numbers[numbers.length - 1]; | |
| for (let i = numbers.length; i < 30000000; i++) { | |
| newNumber = computeNewNumber(newNumber); | |
| const entry = cache[newNumber]; | |
| if (entry) { | |
| if (entry.lastSpoken === -1) { | |
| entry.lastSpoken = i + 1; | |
| } else { | |
| entry.previousSpoken = entry.lastSpoken; | |
| entry.lastSpoken = i + 1; | |
| } | |
| } else { | |
| cache[newNumber] = { lastSpoken: i + 1, previousSpoken: -1 }; | |
| } | |
| } | |
| return newNumber; | |
| } | |
| console.time("day15_part2"); | |
| const result = day15_part2([7, 14, 0, 17, 11, 1, 2]); | |
| console.timeEnd("day15_part2"); | |
| console.log(result); |
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