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#include "aoc.h"
#include <vector>
namespace aoc2020 {
struct pos {
int x;
int y;
};
pos mov(pos p, int dx, int dy) { return {p.x + dx, p.y + dy}; }
void progress(pos p, pos* d1, pos* d2, int dx, const std::vector<line_view>& trees, int* count) {
pos* d = dx > 0 ? d2 : d1;
pos n = mov(p, d->x, d->y);
if (size_t(n.y) < trees.size()) {
const line_view& row = trees[n.y];
if (size_t(n.x) < row.length) {
const char* t = row.line + n.x;
if (*t == '#') {
*count += 1;
}
progress(n, d1, d2, 0, trees, count);
} else {
d2->x = n.x - row.length;
d2->y = d1->y;
// printf("delta %d %d\n", d2->x, d2->y);
progress({0, p.y}, d1, d2, 1, trees, count);
}
}
}
std::pair<int, size_t> day3(line_view file) {
std::vector<line_view> trees;
per_line(file, [&trees](line_view lv) {
trees.push_back({lv.line, lv.line + lv.length - 1});
return true;
});
pos d1{3, 1};
pos d2{0, 0};
int count0{0};
progress({0, 0}, &d1, &d2, 0, trees, &count0);
int count1{0};
size_t total{1};
pos ds[] = {{1, 1}, {3, 1}, {5, 1}, {7, 1}, {1, 2}};
for (auto& d : ds) {
progress({0, 0}, &d, &d2, 0, trees, &count1);
total *= count1;
count1 = 0;
}
return {count0, total};
}
} // namespace aoc2020
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