From 36be2b2eb22ba9319a1ae478b612ac91e9e367d1 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Mon, 21 Dec 2020 20:40:05 +0100
Subject: [PATCH] sudoku: constraints: add sudoku rules constraints

---
 meson.build       |  1 +
 src/constraints.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++
 src/constraints.h | 13 ++++++++++++
 3 files changed, 64 insertions(+)
 create mode 100644 src/constraints.c
 create mode 100644 src/constraints.h

diff --git a/meson.build b/meson.build
index dd667dc..ef8e833 100644
--- a/meson.build
+++ b/meson.build
@@ -9,6 +9,7 @@ project(
 )
 
 sources = [
+  'src/constraints.c',
   'src/main.c',
   'src/sudoku.c',
 ]
diff --git a/src/constraints.c b/src/constraints.c
new file mode 100644
index 0000000..c2edcc2
--- /dev/null
+++ b/src/constraints.c
@@ -0,0 +1,50 @@
+#include "constraints.h"
+
+#include "sudoku.h"
+
+bool line_violation(const struct sudoku *grid, size_t i, size_t j) {
+    if (!grid)
+        return true;
+
+    for (size_t l = 0; l < 9; ++l) {
+        if (l == i)
+            continue;
+        if (grid->grid[l][j] == grid->grid[i][j])
+            return true;
+    }
+
+    return false;
+}
+
+bool column_violation(const struct sudoku *grid, size_t i, size_t j) {
+    if (!grid)
+        return true;
+
+    for (size_t c = 0; c < 9; ++c) {
+        if (c == j)
+            continue;
+        if (grid->grid[i][c] == grid->grid[i][j])
+            return true;
+    }
+
+    return false;
+}
+
+bool square_violation(const struct sudoku *grid, size_t i, size_t j) {
+    if (!grid)
+        return true;
+
+    const size_t x = i / 3;
+    const size_t y = j / 3;
+
+    for (size_t l = 3 * x; l < 3 * (x + 1); ++l) {
+        for (size_t c = 3 * y; c < 3 * (y + 1); ++c) {
+            if (l == i && c == j)
+                continue;
+            if (grid->grid[l][c] == grid->grid[i][j])
+                return true;
+        }
+    }
+
+    return false;
+}
diff --git a/src/constraints.h b/src/constraints.h
new file mode 100644
index 0000000..09e73a0
--- /dev/null
+++ b/src/constraints.h
@@ -0,0 +1,13 @@
+#ifndef CONSTRAINTS_H
+#define CONSTRAINTS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+struct sudoku;
+
+bool line_violation(const struct sudoku *grid, size_t i, size_t j);
+bool column_violation(const struct sudoku *grid, size_t i, size_t j);
+bool square_violation(const struct sudoku *grid, size_t i, size_t j);
+
+#endif /* !CONSTRAINTS_H */