1 files changed, 36 insertions, 0 deletions
diff --git a/src/2021/day9/aoc.h b/src/2021/day9/aoc.h
index cd205cd..5e079fe 100644
--- a/src/2021/day9/aoc.h
+++ b/src/2021/day9/aoc.h
@@ -3,4 +3,40 @@
 
 namespace aoc2021 {
 
+struct heightmap {
+  // 0 .. 99
+  char hs[100 * 100] = {0};
+
+  void load(int r, line_view lv) {
+    const char* p = lv.line;
+    for(int i = 0; i < 100; i++) {
+      hs[100 * r + i] = *(p + i) - '0';
+    }
+  }
+
+  void low_point(int x, int y, int* d) const noexcept {
+    char l = x == 0 ? 10 : hs[100 * y + x - 1];
+    char r = x == 99 ? 10 : hs[100 * y + x + 1];
+    char t = y == 0 ? 10 : hs[100 * (y - 1) + x];
+    char b = y == 99 ? 10 : hs[100 * (y + 1) + x];
+
+    char n = hs[100 * y + x];
+    if (n < l && n < r && n < t && n < b) {
+      *d += n + 1;
+    }
+  }
+  
+  int risks() const noexcept {
+    int r{0};
+    for (int y = 0; y < 100; y++) {
+      for (int x = 0; x < 100; x++) {
+        low_point(x, y, &r);
+      }
+    }
+    return r;
+  }
+};
+
+std::pair<int, int> day9(line_view file);
+
 }