From bcc5b5097ef1c5f042986640483c8a8515a43bf2 Mon Sep 17 00:00:00 2001
From: Drew Galbraith <dgalbraith33@gmail.com>
Date: Mon, 17 Apr 2023 16:31:47 -0700
Subject: [PATCH] First pass at a sudoku solver: Puzzle Import

Imports a puzzle from a string and displays the restricted puzzle.
---
 .clang-format     |  1 +
 .gitignore        |  2 ++
 CMakeLists.txt    | 14 ++++++++
 solver.cpp        | 11 ++++++
 solver/cell.cpp   | 17 +++++++++
 solver/cell.h     | 26 ++++++++++++++
 solver/puzzle.cpp | 88 +++++++++++++++++++++++++++++++++++++++++++++++
 solver/puzzle.h   | 20 +++++++++++
 8 files changed, 179 insertions(+)
 create mode 100644 .clang-format
 create mode 100644 .gitignore
 create mode 100644 CMakeLists.txt
 create mode 100644 solver.cpp
 create mode 100644 solver/cell.cpp
 create mode 100644 solver/cell.h
 create mode 100644 solver/puzzle.cpp
 create mode 100644 solver/puzzle.h

diff --git a/.clang-format b/.clang-format
new file mode 100644
index 0000000..f6cb8ad
--- /dev/null
+++ b/.clang-format
@@ -0,0 +1 @@
+BasedOnStyle: Google
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3392a0b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+build/
+builddir/
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..f315f6c
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(Sudoku)
+
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+set(SOURCE_FILES
+  solver/cell.cpp
+  solver/puzzle.cpp
+  solver.cpp
+)
+
+add_executable(solver ${SOURCE_FILES})
diff --git a/solver.cpp b/solver.cpp
new file mode 100644
index 0000000..b71947e
--- /dev/null
+++ b/solver.cpp
@@ -0,0 +1,11 @@
+#include <iostream>
+
+#include "solver/puzzle.h"
+
+int main(int argc, char** argv) {
+  Puzzle puzzle = Puzzle::FromString(
+      "3..4.162.1...8.4....5.2.83..578........7..5.3..29.4..748.53..1.2.3.9...."
+      ".7...6.9.");
+  std::cout << "https://tiramisu.one/sudoku.html?p=" << puzzle.CurrentState()
+            << "&m=" << puzzle.PencilMarkState() << std::endl;
+}
diff --git a/solver/cell.cpp b/solver/cell.cpp
new file mode 100644
index 0000000..c777c10
--- /dev/null
+++ b/solver/cell.cpp
@@ -0,0 +1,17 @@
+#include "cell.h"
+
+#include <cassert>
+
+Cell::Cell()
+    : state_(Unsolved), value_(0), possibilities_{true, true, true, true, true,
+                                                  true, true, true, true} {}
+
+Cell::Cell(uint8_t value)
+    : state_(Solved), value_(value), possibilities_{false, false, false,
+                                                    false, false, false,
+                                                    false, false, false} {}
+
+void Cell::Restrict(uint8_t value) {
+  assert(value >= 1 && value <= 9);
+  possibilities_[value - 1] = false;
+}
diff --git a/solver/cell.h b/solver/cell.h
new file mode 100644
index 0000000..7396577
--- /dev/null
+++ b/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_;
+};
diff --git a/solver/puzzle.cpp b/solver/puzzle.cpp
new file mode 100644
index 0000000..808f8eb
--- /dev/null
+++ b/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() {}
diff --git a/solver/puzzle.h b/solver/puzzle.h
new file mode 100644
index 0000000..c67c2f8
--- /dev/null
+++ b/solver/puzzle.h
@@ -0,0 +1,20 @@
+#pragma once
+
+#include <optional>
+#include <string>
+
+#include "cell.h"
+
+class Puzzle {
+ public:
+  static Puzzle FromString(std::string puzzle);
+
+  std::string CurrentState();
+  std::string PencilMarkState();
+
+  void AssignSquare(uint8_t id, uint8_t value);
+
+ private:
+  Puzzle();
+  std::array<Cell, 81> cells_;
+};