Apply rules to segments as well as rows and columns

solve.c

@@ -120,7 +120,23 @@ int solve(struct sudoku *sud)
 				match = true;
 		}
 
-		/* TODO: Apply rules to each segment. */
+		/* Apply rules to each segment. */
+		for (i = 0; i < NDIGITS; ++i) {
+			for (j = 0; j < NDIGITS; ++j) {
+				r = 3 * (i / 3) + j / 3;
+				c = 3 * (i % 3) + j % 3;
+
+				group[j].row = r;
+				group[j].col = c;
+				group[j].state = &sud->cells[r][c];
+			}
+
+			res = apply_rules(sud, &group);
+			if (res == ERROR)
+				return -1;
+			else if (res == MATCH)
+				match = true;
+		}
 
 		/* Exit if no matches. */
 		if (!match)