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Completed day 13

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Gnarwhal 2020-12-14 15:28:55 -08:00
parent ad1194b817
commit 54e59161c0
Signed by: Gnarwhal
GPG key ID: 0989A73D8C421174
1 changed files with 14 additions and 17 deletions
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31
2020/days/day13.cpp
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@ -32,11 +32,14 @@
#include "../misc/types.hpp"
#include "../misc/print.hpp"
struct Pair{ u64 id; usize index; };
struct Pair{ i64 id; usize index; };
auto find_least(u64 new_base, u64 new_loop, u64 req_base, u64 req_loop, u64 iter) -> u64 {
while ((new_base + ++iter * new_loop - req_base) % req_loop != 0);
return new_base + iter * new_loop;
// f = a + n0 * b = c + n1 * d
// f = req_base + n0 * req_loop = new_base + n1 * new_loop
// Solve for the smallest integer value f such that this holds true
auto find_least(i64 new_base, i64 new_loop, i64 req_base, i64 req_loop, i64 iter) -> i64 {
while ((req_base - new_base + ++iter * req_loop) % new_loop != 0);
return req_base + iter * req_loop;
}
auto day13() -> void {
@ -55,7 +58,7 @@ auto day13() -> void {
while ((end = line.find(',', start)) != std::string::npos) {
id = line.substr(start, end - start);
if (id != "x") {
buses.push_back({ u64(std::stoi(line.substr(start, end - start))), index });
buses.push_back({ i64(std::stoi(line.substr(start, end - start))), index });
}
start = end + 1;
++index;
@ -63,7 +66,7 @@ auto day13() -> void {
end = line.size();
id = line.substr(start, end - start);
if (id != "x") {
buses.push_back({ u64(std::stoi(line.substr(start, end - start))), index });
buses.push_back({ i64(std::stoi(line.substr(start, end - start))), index });
}
}
@ -78,18 +81,12 @@ auto day13() -> void {
}
print((id * minutes));
auto req_base = usize(0);
auto req_loop = usize(1);
auto req_base = usize(buses[0].index);
auto req_loop = usize(buses[0].id );
for (auto i = usize(1); i < buses.size(); ++i) {
auto base_loop = usize(-1);
while ((++base_loop * buses[0].id + buses[i].index) % buses[i].id != 0);
auto rep_loop = usize(0);
while ((++rep_loop * buses[0].id) % buses[i].id != 0);
req_base = find_least(base_loop, rep_loop, req_base, req_loop, -1);
req_base = find_least(-buses[i].index, buses[i].id, req_base, req_loop, -1);
if (i < buses.size() - 1) {
req_loop = find_least(0, rep_loop, 0, req_loop, 0);
req_loop = find_least(0, buses[i].id, 0, req_loop, 0);
}
/*
required_base (rqb), required_loop (rql)
@ -102,5 +99,5 @@ auto day13() -> void {
b0 * rql = b1 * rl < minimize and store in required loop
*/
}
print((req_base * buses[0].id));
print(req_base);
}