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#include "aoc.h"
namespace aoc2016 {
static void reverse(std::string& s) {
size_t b = 0;
size_t e = s.size() - 1;
while (b < e) {
std::swap(s.at(b), s.at(e));
b++;
e--;
}
}
static void replace(std::string& s) {
char s2[] = {'1', '0'};
for (size_t i = 0; i < s.size(); i++) {
s.at(i) = s2[(int)s.at(i) - '0'];
}
}
static std::string take(const std::string& s, size_t n) { return n < s.size() ? std::string{s.data(), n} : s; }
static std::string checksum(const std::string& s) {
std::string x;
char s2[] = {'0', '1'};
for (size_t i = 0; i < s.size() - 1; i += 2) {
x.push_back(s2[(int)s.at(i) == s.at(i + 1)]);
}
return x;
}
std::string checksum(std::string s, size_t max) {
while (s.length() < max) {
std::string a{s};
reverse(a);
replace(a);
s.push_back('0');
s.append(a);
}
s = take(s, max);
auto chk = checksum(s);
while ((chk.size() & 1) == 0) {
chk = checksum(chk);
}
return chk;
}
std::pair<std::string, std::string> day16(line_view) {
std::string init{"11110010111001001"};
return {checksum(init, 272), checksum(init, 35651584)};
}
} // namespace aoc2016
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