42 lines
1.4 KiB
C++
42 lines
1.4 KiB
C++
#include <string>
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#include <iostream>
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#include <cstdlib>
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int main() {
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std::string line;
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std::getline(std::cin, line);
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auto target{std::stoul(line)};
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/* This is a really stupid way to do this in terms of effort, but it produces the right answer and doesn't involve
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* thinking too much:
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*
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* n is the current house we're at.
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*/
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for (auto n{2UL}; true; ++n) {
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auto amt{0UL};
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/* Find the number of presents delivered to house `n`. We do this by walking through all numbers <= sqrt(n) and
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* seeing if they are a factor. If so we add presents for that number (i) and also (n/i), being careful not to
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* double count for square roots. This reduces the amount of work we have to do significantly.
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*
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* For the second part we also check to ensure we've not at the 51st delivery or greater for this elf.
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*/
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for (auto i{1UL}; i <= (n / i); ++i) {
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if (n % i == 0) {
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auto i2{n / i};
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if (i2 <= 50) {
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amt += i * 11;
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}
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if (i <= 50 && i != i2) {
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amt += i2 * 11;
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}
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}
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}
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if (amt >= target) {
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std::cout << "Target: " << target << " met at: " << n << " with amount: " << amt << '\n';
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return EXIT_SUCCESS;
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}
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}
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return EXIT_FAILURE;
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} |