Applied OnlyCellStrategy-Backtracking fix

The fix for issue #56 was already present in non-killer Sudoku in
v0.2.0, but never noticed.
This PR pushes the fix for this bug in a successor of v0.2.0.

src/fix_tests.rs

@@ -0,0 +1,34 @@
+use crate::{Sudoku, SudokuGrid};
+use crate::constraint::DefaultConstraint;
+use crate::solver::{Solution, Solver};
+use crate::solver::strategy::{
+    OnlyCellStrategy,
+    StrategicBacktrackingSolver
+};
+
+#[test]
+fn only_cell_strategic_backtracking() {
+    let sudoku = Sudoku::parse("3x3;
+         , , , , ,7,3, , ,\
+         ,1,2, , , ,5,4, ,\
+         , ,3,4, , , ,1, ,\
+         , ,5,6, , , ,8, ,\
+         , , , , , , , , ,\
+        7, , , , ,2,4, , ,\
+        6,4,1, , , ,8, , ,\
+        5,3, , , ,6,7, , ,\
+         , , , , ,9, , , ", DefaultConstraint).unwrap();
+    let solver = StrategicBacktrackingSolver::new(OnlyCellStrategy);
+    let expected = SudokuGrid::parse("3x3;
+        4,5,6,2,1,7,3,9,8,\
+        8,1,2,9,6,3,5,4,7,\
+        9,7,3,4,5,8,6,1,2,\
+        1,2,5,6,7,4,9,8,3,\
+        3,6,4,8,9,1,2,7,5,\
+        7,9,8,5,3,2,4,6,1,\
+        6,4,1,7,2,5,8,3,9,\
+        5,3,9,1,8,6,7,2,4,\
+        2,8,7,3,4,9,1,5,6").unwrap();
+
+    assert_eq!(Solution::Unique(expected), solver.solve(&sudoku));
+}

src/lib.rs

@@ -225,6 +225,9 @@ pub mod generator;
 pub mod solver;
 pub mod util;
 
+#[cfg(test)]
+mod fix_tests;
+
 use constraint::Constraint;
 use error::{SudokuError, SudokuParseError, SudokuParseResult, SudokuResult};
 

src/solver/strategy/solvers.rs

@@ -130,15 +130,8 @@ impl<S: Strategy> StrategicBacktrackingSolver<S> {
 
         for number in options {
             let mut sudoku_info = sudoku_info.clone();
-            sudoku_info
-                .enter_cell_no_update(min_options_column, min_options_row, number)
+            sudoku_info.enter_cell(min_options_column, min_options_row, number)
                 .unwrap();
-            let options_info = sudoku_info
-                .get_options_mut(min_options_column, min_options_row)
-                .unwrap();
-            options_info.clear();
-            options_info.insert(number).unwrap();
-
             let next_solution = self.solve_rec(&mut sudoku_info);
             solution = solution.union(next_solution);