2021 day3 part1

1 files changed, 41 insertions, 0 deletions

diff --git a/src/2021/day3/aoc.cpp b/src/2021/day3/aoc.cpp
index 7a3c895..dc3d349 100644
--- a/src/2021/day3/aoc.cpp
+++ b/src/2021/day3/aoc.cpp
@@ -2,4 +2,45 @@
 
 namespace aoc2021 {
 
+int decimal(const char* p) {
+  int d{0};
+  while (*p == '0' || *p == '1') {
+    d = 2 * d + *p - '0';
+    p++;
+  }
+  return d;
 }
+
+int day3(line_view file) {
+  char gamma[13] = {0};
+  char epsilon[13] = {0};
+
+  int is[12] = {0};
+  int total{0};
+  per_line(file, [&is, &total](line_view lv) {
+    for (int i = 0; i < 12; i++) {
+      if (*(lv.line + i) == '1') {
+        is[i] += 1;
+      }
+    }
+    total += 1;
+    return true;
+  });
+
+  for (int i = 0; i < 12; i++) {
+    if (is[i] > total / 2) {
+      gamma[i] = '1';
+      epsilon[i] = '0';
+    } else {
+      gamma[i] = '0';
+      epsilon[i] = '1';
+    }
+  }
+
+  // printf("%s\n", gamma);
+  // printf("%s\n", epsilon);
+
+  return decimal(gamma) * decimal(epsilon);
+}
+
+} // namespace aoc2021