First pass at a sudoku solver: Puzzle Import

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

solver/puzzle.cpp

@@ -0,0 +1,88 @@
+#include "puzzle.h"
+
+#include <cassert>
+#include <iostream>
+#include <sstream>
+
+namespace {
+
+uint8_t RowStart(uint8_t id) { return (id / 9) * 9; }
+uint8_t ColStart(uint8_t id) { return id % 9; }
+uint8_t BoxStart(uint8_t id) {
+  uint8_t row = (RowStart(id) / 27) * 27;
+  uint8_t col = (ColStart(id) / 3) * 3;
+  return row + col;
+}
+
+constexpr std::array<uint8_t, 9> kBoxOffsets{0, 1, 2, 9, 10, 11, 18, 19, 20};
+
+}  // namespace
+
+Puzzle Puzzle::FromString(std::string puzzle) {
+  assert(puzzle.length() == 81);
+  Puzzle p;
+
+  for (int i = 0; i < 81; i++) {
+    if (puzzle[i] == '.' || puzzle[i] == '0') {
+      continue;
+    }
+    int diff = puzzle[i] - '0';
+    if (diff < 1 || diff > 9) {
+      assert(false && "Invalid input character");
+    }
+    p.AssignSquare(i, diff);
+  }
+  return p;
+}
+
+std::string Puzzle::CurrentState() {
+  std::ostringstream str;
+  for (const Cell& c : cells_) {
+    if (c.IsSolved()) {
+      str << (int)c.value();
+    } else {
+      str << '.';
+    }
+  }
+  return str.str();
+}
+
+std::string Puzzle::PencilMarkState() {
+  std::ostringstream str;
+  for (const Cell& c : cells_) {
+    for (uint8_t i = 1; i <= 9; i++) {
+      if (c.IsPossible(i)) {
+        str << (int)i;
+      }
+    }
+    str << ",";
+  }
+  // Erase the trailing ",".
+  std::string temp = str.str();
+  temp.erase(temp.end() - 1);
+  return temp;
+}
+
+void Puzzle::AssignSquare(uint8_t id, uint8_t value) {
+  assert(id < 81);
+  assert(value >= 0 && value <= 9);
+
+  cells_[id] = Cell(value);
+
+  const uint8_t row = RowStart(id);
+  for (uint8_t i = row; i < row + 9; i++) {
+    cells_[i].Restrict(value);
+  }
+
+  const uint8_t col = ColStart(id);
+  for (uint8_t i = col; i < 81; i += 9) {
+    cells_[i].Restrict(value);
+  }
+
+  uint8_t box = BoxStart(id);
+  for (uint8_t offset : kBoxOffsets) {
+    cells_[box + offset].Restrict(value);
+  }
+}
+
+Puzzle::Puzzle() {}