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Tidy up 2021 day 3 puzzle 2 code.

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This adds some comments and removes code duplication.
This commit is contained in:
Matthew Gretton-Dann
2021-12-03 12:32:15 +00:00
parent b43c4a617e
commit b6213c6593
1 changed files with 24 additions and 30 deletions
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54
2021/puzzle-03-02.cc
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@@ -8,18 +8,35 @@
#include <string>
#include <vector>
/** \brief Convert the string s to a number
* @param s String of 1s and 0s to convert
* @return Value of string
*/
auto to_num(std::string const& s) -> std::uint64_t
{
std::uint64_t result{0};
for (auto c : s) {
assert(c == '1' || c == '0');
result <<= 1;
result |= (c == '1' ? 1 : 0);
result |= (c == '1') ? 1 : 0;
}
return result;
}
auto find_oxygen_rating(std::vector<std::string> const& lines) -> std::string
/** \brief Find the rating for a given selector and set of lines.
*
* @tparam Fn Selector function type
* @param lines Lines to select from
* @param selector Takes bool saying whether ones are predominant, should return character to keep.
* @return String of selected number.
*/
template<typename Fn>
auto find_rating(std::vector<std::string> const& lines, Fn selector) -> std::string
{
/* Algorithm description: We copy the given lines and then for each index in the strings in turn
* we see how many 1 digits are in that index. The function \a selector is then called to get the
* character to keep, before erasing the strings we do not want to keep.
*/
std::vector<std::string> data{lines};
assert(!data.empty());
std::size_t len{data[1].size()};
@@ -27,32 +44,7 @@ auto find_oxygen_rating(std::vector<std::string> const& lines) -> std::string
auto one_bits{std::accumulate(
data.begin(), data.end(), std::uint64_t{0},
[i](std::uint64_t a, std::string const& s) { return a + (s[i] == '1' ? 1 : 0); })};
char keep{(one_bits * 2 >= data.size()) ? '1' : '0'};
std::cout << "Size of data = " << data.size() << " Number of one bits = " << one_bits
<< " keeping " << keep << '\n';
auto it{std::remove_if(data.begin(), data.end(),
[keep, i](std::string const& s) { return s[i] != keep; })};
data.erase(it, data.end());
if (data.size() <= 1) {
break;
}
}
assert(data.size() == 1);
return data[0];
}
auto find_co2_rating(std::vector<std::string> const& lines) -> std::string
{
std::vector<std::string> data{lines};
assert(!data.empty());
std::size_t len{data[1].size()};
for (std::size_t i{0}; i < len; ++i) {
auto one_bits{std::accumulate(
data.begin(), data.end(), std::uint64_t{0},
[i](std::uint64_t a, std::string const& s) { return a + (s[i] == '1' ? 1 : 0); })};
char keep{(one_bits * 2 >= data.size()) ? '0' : '1'};
std::cout << "Size of data = " << data.size() << " Number of one bits = " << one_bits
<< " keeping " << keep << '\n';
char keep{selector(one_bits * 2 >= data.size())};
auto it{std::remove_if(data.begin(), data.end(),
[keep, i](std::string const& s) { return s[i] != keep; })};
data.erase(it, data.end());
@@ -72,8 +64,10 @@ auto main() -> int
lines.push_back(line);
}
auto oxygen_rating{to_num(find_oxygen_rating(lines))};
auto co2_rating{to_num(find_co2_rating(lines))};
auto oxygen_rating{
to_num(find_rating(lines, [](bool mostly_ones) { return mostly_ones ? '1' : '0'; }))};
auto co2_rating{
to_num(find_rating(lines, [](bool mostly_ones) { return mostly_ones ? '0' : '1'; }))};
std::cout << "Oxygen generator rating * CO2 scrubber rating = " << oxygen_rating << " * "
<< co2_rating << " = " << oxygen_rating * co2_rating << '\n';