2020 day1 two sum

1 files changed, 36 insertions, 1 deletions

diff --git a/src/2020/day1/aoc.cpp b/src/2020/day1/aoc.cpp
index a57fb7c..87972e7 100644
--- a/src/2020/day1/aoc.cpp
+++ b/src/2020/day1/aoc.cpp
@@ -1,3 +1,38 @@
 #include "aoc.h"
+#include <set>
+#include <vector>
 
-namespace aoc2020 {}
+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(const std::vector<int>& is, int target) {
+  std::set<int> pairs;
+  for (auto i : is) {
+    auto it = pairs.find(i);
+    if (it == pairs.end()) {
+      pairs.insert(target - i);
+    } else {
+      return i * (target - *it);
+    }
+  };
+  return 0;
+}
+
+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, target);
+}
+
+} // namespace aoc2020