2020 day3 part1

1 files changed, 43 insertions, 0 deletions

diff --git a/src/2020/day3/aoc.cpp b/src/2020/day3/aoc.cpp
index 849bad9..e135988 100644
--- a/src/2020/day3/aoc.cpp
+++ b/src/2020/day3/aoc.cpp
@@ -1,5 +1,48 @@
 #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);
+    }
+  }
 }
+
+int 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 count{0};
+  progress({0, 0}, &d1, &d2, 0, trees, &count);
+
+  return count;
+}
+
+} // namespace aoc2020