cc192: switch to a stride based implementation.

cc192.cc

@@ -1,4 +1,5 @@
-// Design an algorithm to figure out if someone has won in a game of tic-tac-toe.
+// Design an algorithm to figure out if someone has won in a game of
+// tic-tac-toe.
 
 #define CATCH_CONFIG_MAIN
 #include <catch.hpp>
@@ -8,61 +9,51 @@
 enum class Owner {
   Invalid = 0,
   None = 1,
-    X = 2,
-    O = 4,
+  X = 2,
+  O = 4,
 };
 
-using Row = std::array<Owner, 3>;
-using Board = std::array<Row, 3>;
+static const int Dim = 3;
 
-static Owner merge(std::initializer_list<Owner> items) {
+using Row = std::array<Owner, Dim>;
+using Board = std::array<Row, Dim>;
+
+static bool is_winner(const Board& board, int x, int y, int dx, int dy) {
   int merged = 0;
 
-  for (auto item: items) {
-    merged |= int(item);
+  for (auto i = 0; i < Dim; i++) {
+    merged |= int(board[y+i*dy][x+i*dx]);
   }
-  return Owner(merged);
-}
-
-static bool is_winner(Owner owner) {
+  auto owner = Owner(merged);
   return owner == Owner::X || owner == Owner::O;
 }
 
 static bool has_winner(const Board& board) {
-  Owner winner = Owner::Invalid;
-
-  for (const auto& row: board) {
-    if (is_winner(merge({row[0], row[1], row[2]}))) {
-      return true;
-    }
-  }
-  for (size_t x = 0; x < board[0].size(); x++) {
-    if (is_winner(merge({board[0][x], board[1][x], board[2][x]}))) {
-      return true;
-    }
-  }
-  if (is_winner(merge({board[0][0], board[1][1], board[2][2]}))) {
-    return true;
-  }
-  if (is_winner(merge({board[2][0], board[1][1], board[0][2]}))) {
-    return true;
-  }
-
-  return false;
+  return false
+      // Columns
+      || is_winner(board, 0, 0, 1, 0)
+      || is_winner(board, 0, 1, 1, 0)
+      || is_winner(board, 0, 2, 1, 0)
+      // Rows
+      || is_winner(board, 0, 0, 0, 1)
+      || is_winner(board, 1, 0, 0, 1)
+      || is_winner(board, 2, 0, 0, 1)
+      // Diagonals
+      || is_winner(board, 0, 0, 1, 1)
+      || is_winner(board, 2, 0, -1, 1)
+      ;
 }
 
-Board make_board(std::string defn) {
+static Board make_board(const std::string& defn) {
   Board board;
   int x = 0;
   int y = 0;
 
   for (auto& row : board) {
-    for (auto& cell: row) {
-      cell = Owner::None;
-    }
+    row.fill(Owner::None);
   }
 
-  for (auto ch: defn) {
+  for (auto ch : defn) {
     switch (ch) {
       case 'x':
         board[y][x] = Owner::X;
@@ -73,7 +64,7 @@ Board make_board(std::string defn) {
       default:
         board[y][x] = Owner::None;
     }
-    if (++x == 3) {
+    if (++x == Dim) {
       x = 0;
       y++;
     }