1 files changed, 99 insertions, 0 deletions

diff --git a/2016/src/day07.cpp b/2016/src/day07.cpp
new file mode 100644
index 0000000..faa306f
--- /dev/null
+++ b/2016/src/day07.cpp
@@ -0,0 +1,99 @@
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+read_file(string_view filename)
+{
+        fstream input{ filename };
+
+        vector<string> lines;
+
+        for ( string line; getline(input, line); ) {
+                lines.emplace_back(line);
+        }
+
+        return lines;
+}
+
+void
+part1(const vector<string>& lines)
+{
+        long sum = 0;
+        for ( const auto& line: lines ) {
+                long found_inner = 0;
+                long found_outer = 0;
+
+                bool inner = false;
+                for ( size_t i = 0; i + 3 < line.length(); ++i ) {
+                        if ( line[i] == '[' ) {
+                                inner = true;
+                        }
+                        if ( line[i] == ']' ) {
+                                inner = false;
+                        }
+
+                        if ( line[i + 0] == line[i + 3] && line[i + 0] != line[i + 1] && line[i + 1] == line[i + 2] ) {
+                                if ( inner ) {
+                                        ++found_inner;
+                                }
+                                else {
+                                        ++found_outer;
+                                }
+                        }
+                }
+                sum += (found_inner == 0 && found_outer != 0) ? 1 : 0;
+        }
+        cout << sum << endl;
+}
+
+void
+part2(const vector<string>& lines)
+{
+        long sum = 0;
+        for ( const auto& line: lines ) {
+                set<tuple<char, char>> inners;
+                set<tuple<char, char>> outers;
+
+                bool inner = false;
+                for ( size_t i = 0; i + 2 < line.length(); ++i ) {
+                        if ( line[i] == '[' ) {
+                                inner = true;
+                        }
+                        if ( line[i] == ']' ) {
+                                inner = false;
+                        }
+
+                        if ( line[i + 0] == line[i + 2] && line[i + 0] != line[i + 1] ) {
+                                if ( inner ) {
+                                        inners.emplace(line[i + 0], line[i + 1]);
+                                        if ( outers.contains({ line[i + 1], line[i + 0] }) ) {
+                                                ++sum;
+                                                break;
+                                        }
+                                }
+                                else {
+                                        outers.emplace(line[i + 0], line[i + 1]);
+                                        if ( inners.contains({ line[i + 1], line[i + 0] }) ) {
+                                                ++sum;
+                                                break;
+                                        }
+                                }
+                        }
+                }
+        }
+        cout << sum << endl;
+}
+
+int
+main()
+{
+        auto lines = read_file("data/day07.txt");
+        part1(lines);
+        part2(lines);
+}