From 5b01700650004ded216dd7cc94527e77e1990bde Mon Sep 17 00:00:00 2001
From: Alberto Venturini <aventurini@gmail.com>
Date: Tue, 29 Oct 2019 21:42:13 +0200
Subject: [PATCH] Add valid? method

---
 spec/board_spec.cr | 11 +++++++++++
 src/board.cr       | 10 ++++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/spec/board_spec.cr b/spec/board_spec.cr
index aa53a45..75cb232 100644
--- a/spec/board_spec.cr
+++ b/spec/board_spec.cr
@@ -42,4 +42,15 @@ describe Sudoku::Board do
     board.extract_block(3, 1).should eq [[42, 43], [44, 45]]
   end
 
+  it "validates cells correctly" do
+    board = Sudoku::Board.new(9, 3)
+    board.put(1, 0, 0)
+    board.put(2, 0, 1)
+    board.put(3, 1, 0)
+    board.valid?(4, 0, 2).should be_true
+    board.valid?(4, 2, 0).should be_true
+    board.valid?(3, 0, 2).should be_false
+    board.valid?(3, 2, 0).should be_false
+  end
+
 end
diff --git a/src/board.cr b/src/board.cr
index 7dcd152..24da810 100644
--- a/src/board.cr
+++ b/src/board.cr
@@ -24,8 +24,14 @@ module Sudoku
       @grid[y][x]
     end
 
-    def check_valid(value : Value, x, y)
-
+    def valid?(value : Value, x, y)
+      if value == nil
+        true
+      else
+        extract_row(y).all? { |i| i != value } &&
+        extract_column(x).all? { |i| i != value } &&
+        extract_block(x, y).all? { |i| i.all? { |j| j != value } }
+      end
     end
 
     def extract_row(y)