First pass at a sudoku solver: Puzzle Import

Imports a puzzle from a string and displays the restricted puzzle.

solver/cell.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <stdint.h>
+
+#include <array>
+
+class Cell {
+ public:
+  enum State {
+    Unsolved,
+    Solved,
+  };
+  Cell();
+  explicit Cell(uint8_t value);
+
+  void Restrict(uint8_t value);
+
+  bool IsSolved() const { return state_ == Solved; }
+  uint8_t value() const { return value_; }
+  bool IsPossible(uint8_t v) const { return possibilities_[v - 1]; }
+
+ private:
+  State state_;
+  uint8_t value_;
+  std::array<bool, 9> possibilities_;
+};