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#include "aoc.h"
#include <set>
#include <utility>
#include <vector>
namespace aoc2020 {
int get_number(const char* p) {
int d{0};
while (*p >= '0' && *p <= '9') {
d = d * 10 + *p - '0';
p++;
}
return d;
}
int two_sum(int* is, size_t s, int target) {
std::set<int> pairs;
for (size_t i = 0; i < s; i++) {
auto it = pairs.find(is[i]);
if (it == pairs.end()) {
pairs.insert(target - is[i]);
} else {
return is[i] * (target - *it);
}
};
return 0;
}
int three_sum(std::vector<int>& is, int target) {
for (size_t i = 0; i < is.size(); i++) {
std::swap(is[0], is[i]);
int x = two_sum(&is[1], is.size() - 1, target - is[0]);
if (x > 0) {
return is[0] * x;
}
}
return 0;
}
std::pair<int, int> day1(line_view file, int target) {
std::vector<int> is;
per_line(file, [&is](line_view lv) {
is.emplace_back(get_number(lv.line));
return true;
});
return {two_sum(is.data(), is.size(), target), three_sum(is, target)};
}
} // namespace aoc2020
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