Split out results structure

We now return the results in a separate structure to the grid we have
been working on.

This ultimately makes it easier to play with the implementation of the
solution finder.

main.cc

@@ -57,6 +57,78 @@ namespace {
     int length_; ///< Side length
   };
 
+  /** Structure holding the results.
+   */
+  struct Results {
+    Results(int length, std::vector<Square> squares) : length_(length), squares_(std::move(squares)) {
+    }
+
+    Results(Results const &other) noexcept = delete;
+    Results &operator=(Results const &other) noexcept = delete;
+    Results &operator=(Results &&other) noexcept = default;
+    Results(Results &&other) noexcept = default;
+    ~Results() noexcept = default;
+
+    auto length() const noexcept -> int { return length_; }
+
+    /** Output the grid. */
+    auto output() const -> void {
+      std::string out;
+      out.resize(length_ * length_);
+      for (auto const& sq : squares_) {
+        prettify_sq(out, sq);
+      }
+      for (auto idx = 0; idx < length_ * length_; idx += length_) {
+        std::cout << std::string_view(out.data() + idx, length_) << '\n';
+      }
+    }
+
+  private:
+    auto set(std::string& s, int x, int y, char c) const noexcept -> void {
+      assert(x < length_);
+      assert(y < length_);
+      assert(grid_[x + y * length_] != c);
+      s[x + y * length_] = c;
+    }
+
+    auto prettify_sq(std::string& s, Square const &sq) const noexcept -> void {
+      switch (sq.length()) {
+        case 1: set(s, sq.x(), sq.y(), '*');
+          break;
+        case 2: set(s, sq.x(), sq.y(), '+');
+          set(s, sq.x() + 1, sq.y(), '+');
+          set(s, sq.x(), sq.y() + 1, '+');
+          set(s, sq.x() + 1, sq.y() + 1, '+');
+          break;
+        default: {
+          auto n = sq.length();
+          set(s, sq.x(), sq.y(), '+');
+          set(s, sq.x() + n - 1, sq.y(), '+');
+          set(s, sq.x(), sq.y() + n - 1, '+');
+          set(s, sq.x() + n - 1, sq.y() + n - 1, '+');
+          for (int i = 1; i < n - 1; ++i) {
+            set(s, sq.x() + i, sq.y(), '-');
+            set(s, sq.x() + i, sq.y() + n - 1, '-');
+            set(s, sq.x(), sq.y() + i, '|');
+            for (int j = 1; j < n - 1; ++j) {
+              set(s, sq.x() + j, sq.y() + i, ' ');
+            }
+            set(s, sq.x() + n - 1, sq.y() + i, '|');
+          }
+
+          int i = sq.x() + n - 1;
+          while (n != 0) {
+            set(s, --i, sq.y() + 1, '0' + (n % 10));
+            n /= 10;
+          }
+        }
+      }
+    }
+
+    int length_;
+    std::vector<Square> squares_;
+  };
+
   /** An N * N grid of characters. */
   struct Grid {
     /** Construct a grid of given side-length. */
@@ -94,22 +166,6 @@ namespace {
       }
     }
 
-    auto prettify() noexcept -> void {
-      for (auto idx = 0; idx < grid_.size(); ++idx) {
-        if (grid_[idx] < 32) {
-          auto const pos = std::make_pair(idx % length_, idx / length_);
-          prettify_sq(Square(pos, grid_[idx]));
-        }
-      }
-    }
-
-    /** Output the grid. */
-    auto output() const -> void {
-      for (auto idx = 0; idx < length_ * length_; idx += length_) {
-        std::cout << std::string_view(grid_.data() + idx, length_) << '\n';
-      }
-    }
-
     /** \brief Get length of the largest square that fits at \a pos in the grid.
      */
     auto largest_square(Pos const &pos, int n) const noexcept -> int {
@@ -147,39 +203,6 @@ namespace {
     }
 
   private:
-    auto prettify_sq(Square const &sq) noexcept -> void {
-      switch (sq.length()) {
-        case 1: set(sq.x(), sq.y(), '*');
-          break;
-        case 2: set(sq.x(), sq.y(), '+');
-          set(sq.x() + 1, sq.y(), '+');
-          set(sq.x(), sq.y() + 1, '+');
-          set(sq.x() + 1, sq.y() + 1, '+');
-          break;
-        default: {
-          auto n = sq.length();
-          set(sq.x(), sq.y(), '+');
-          set(sq.x() + n - 1, sq.y(), '+');
-          set(sq.x(), sq.y() + n - 1, '+');
-          set(sq.x() + n - 1, sq.y() + n - 1, '+');
-          for (int i = 1; i < n - 1; ++i) {
-            set(sq.x() + i, sq.y(), '-');
-            set(sq.x() + i, sq.y() + n - 1, '-');
-            set(sq.x(), sq.y() + i, '|');
-            for (int j = 1; j < n - 1; ++j) {
-              set(sq.x() + j, sq.y() + i, ' ');
-            }
-            set(sq.x() + n - 1, sq.y() + i, '|');
-          }
-
-          int i = sq.x() + n - 1;
-          while (n != 0) {
-            set(--i, sq.y() + 1, '0' + (n % 10));
-            n /= 10;
-          }
-        }
-      }
-    }
 
     /** Set the grid position (x, y) to the character c.
      *
@@ -209,7 +232,7 @@ namespace {
    *
    * Returns the grid of the solution.
    */
-  auto find_solution(int const n) noexcept -> Grid {
+  auto find_solution(int const n) noexcept -> Results {
     /* Implementation is iterative, as opposed to recursive.
      *
      * The recursive implementation is easier to understand - but is
@@ -277,8 +300,7 @@ namespace {
       if (x(pos) == 0 && y(pos) == grid.length()) { break; }
     }
 
-    grid.prettify();
+    return Results(length, sqs);
-    return grid;
   }
 } // anon namespace