Add a Box-Line Reduction Strategy.

src/board.rs

@@ -8,6 +8,20 @@ pub struct Board {
     pub squares: [Square; 81],
 }
 
+pub fn index_to_row(index: u8) -> u8 {
+    index / 9
+}
+
+pub fn index_to_col(index: u8) -> u8 {
+    index % 9
+}
+
+pub fn index_to_box(index: u8) -> u8 {
+    let row = index / 27;
+    let col = (index % 9) / 3;
+    (row * 3) + col
+}
+
 impl Board {
     pub fn from_string(str: &str) -> Board {
         if str.len() != 81 {
@@ -58,9 +72,7 @@ impl Board {
     }
 
     pub fn box_from_index(&self, index: u8) -> SquareIter {
-        let row = index / 27;
-        let col = (index % 9) / 3;
-        SquareIter::from_box(&self.squares, (row * 3) + col)
+        SquareIter::from_box(&self.squares, index_to_box(index))
     }
 
     pub fn boxn(&self, boxn: u8) -> SquareIter {

src/solver/solver.rs

@@ -1,5 +1,5 @@
 use crate::board::Board;
-use crate::strategy::{HiddenSingle, NakedSingle, Strategy, StrategyFn};
+use crate::strategy::{BoxLine, HiddenSingle, NakedSingle, Strategy, StrategyFn};
 use crate::validator;
 
 fn try_strategies(strategies: &[StrategyFn], sudoku_board: &Board) -> Option<Box<dyn Strategy>> {
@@ -21,10 +21,15 @@ pub fn solve_board(mut sudoku_board: Board) -> Result<Board, Board> {
         );
     }
 
-    let strategies: [StrategyFn; 2] = [NakedSingle::find_instance, HiddenSingle::find_instance];
+    let strategies: [StrategyFn; 3] = [
+        NakedSingle::find_instance,
+        HiddenSingle::find_instance,
+        BoxLine::find_instance,
+    ];
 
-    while let Some(ns) = try_strategies(&strategies, &sudoku_board) {
-        sudoku_board = ns.apply(sudoku_board);
+    while let Some(strat) = try_strategies(&strategies, &sudoku_board) {
+        println!("{}", strat);
+        sudoku_board = strat.apply(sudoku_board);
 
         if let validator::BoardState::Broken(ind) = validator::validate_board(&sudoku_board) {
             println!("{}", sudoku_board.to_url());

src/strategy/base.rs

@@ -1,8 +1,10 @@
+use core::fmt;
+
 use crate::board::Board;
 
 pub type StrategyFn = fn(&Board) -> Option<Box<dyn Strategy>>;
 
-pub trait Strategy {
+pub trait Strategy: fmt::Display {
     fn find_instance(board: &Board) -> Option<Box<dyn Strategy>>
     where
         Self: Sized;

src/strategy/box_line.rs

@@ -0,0 +1,163 @@
+use std::fmt::Display;
+
+use crate::{
+    board::{index_to_box, index_to_col, index_to_row, Board},
+    square::Square,
+    strategy::Strategy,
+};
+
+enum Seen {
+    NotSeen,
+    SeenInBox(u8),
+    SeenInMultiple,
+}
+
+pub enum RowCol {
+    Row(u8),
+    Col(u8),
+}
+
+pub struct BoxLine {
+    rowcol: RowCol,
+    boxn: u8,
+    value: u8,
+}
+
+impl Strategy for BoxLine {
+    fn find_instance(board: &Board) -> Option<Box<dyn Strategy>> {
+        for r in 0..9 {
+            for n in 1..=9 {
+                let seen = board
+                    .row(r)
+                    .fold(Seen::NotSeen, |curr, square| match square {
+                        Square::Marks(i, opts) => {
+                            if opts.get(n as usize) {
+                                let boxn = index_to_box(i);
+                                match curr {
+                                    Seen::NotSeen => Seen::SeenInBox(boxn),
+                                    Seen::SeenInBox(b) => {
+                                        if b == boxn {
+                                            curr
+                                        } else {
+                                            Seen::SeenInMultiple
+                                        }
+                                    }
+                                    _ => Seen::SeenInMultiple,
+                                }
+                            } else {
+                                curr
+                            }
+                        }
+                        _ => curr,
+                    });
+
+                match seen {
+                    Seen::SeenInBox(b) => {
+                        if board.boxn(b).any(|sq| match sq {
+                            Square::Marks(i, marks) => {
+                                (index_to_row(i) != r) && marks.get(n as usize)
+                            }
+                            _ => false,
+                        }) {
+                            return Some(Box::new(BoxLine {
+                                rowcol: RowCol::Row(r),
+                                boxn: b,
+                                value: n,
+                            }));
+                        }
+                    }
+                    _ => {}
+                }
+            }
+        }
+        for c in 0..9 {
+            for n in 1..=9 {
+                let seen = board
+                    .col(c)
+                    .fold(Seen::NotSeen, |curr, square| match square {
+                        Square::Marks(i, opts) => {
+                            if opts.get(n as usize) {
+                                let boxn = index_to_box(i);
+                                match curr {
+                                    Seen::NotSeen => Seen::SeenInBox(boxn),
+                                    Seen::SeenInBox(b) => {
+                                        if b == boxn {
+                                            curr
+                                        } else {
+                                            Seen::SeenInMultiple
+                                        }
+                                    }
+                                    _ => Seen::SeenInMultiple,
+                                }
+                            } else {
+                                curr
+                            }
+                        }
+                        _ => curr,
+                    });
+
+                match seen {
+                    Seen::SeenInBox(b) => {
+                        if board.boxn(b).any(|sq| match sq {
+                            Square::Marks(i, marks) => {
+                                (index_to_col(i) != c) && marks.get(n as usize)
+                            }
+                            _ => false,
+                        }) {
+                            return Some(Box::new(BoxLine {
+                                rowcol: RowCol::Col(c),
+                                boxn: b,
+                                value: n,
+                            }));
+                        }
+                    }
+                    _ => {}
+                }
+            }
+        }
+        None
+    }
+
+    fn apply(&self, mut board: Board) -> Board {
+        for ref mut square in board.squares.iter_mut() {
+            if let Square::Marks(i, ref mut marks) = square {
+                if index_to_box(*i as u8) == self.boxn {
+                    match self.rowcol {
+                        RowCol::Row(r) => {
+                            if index_to_row(*i) != r {
+                                marks.set(self.value as usize, false);
+                            }
+                        }
+                        RowCol::Col(c) => {
+                            if index_to_col(*i) != c {
+                                marks.set(self.value as usize, false);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        board
+    }
+}
+
+impl Display for BoxLine {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self.rowcol {
+            RowCol::Row(r) => write!(
+                f,
+                "Box Line Reduction on {} in row {} in box {}",
+                self.value,
+                r + 1,
+                self.boxn + 1,
+            ),
+            RowCol::Col(c) => write!(
+                f,
+                "Box Line Reduction on {} in col {} in box {}",
+                self.value,
+                c + 1,
+                self.boxn + 1,
+            ),
+        }
+    }
+}

src/strategy/hidden_single.rs

@@ -1,4 +1,6 @@
-use crate::board::Board;
+use std::fmt::Display;
+
+use crate::board::{index_to_col, index_to_row, Board};
 use crate::square::Square;
 use crate::strategy::Strategy;
 
@@ -99,3 +101,15 @@ impl Strategy for HiddenSingle {
         board
     }
 }
+
+impl Display for HiddenSingle {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "Hidden Single {} at row {} col {}",
+            self.value,
+            index_to_row(self.index) + 1,
+            index_to_col(self.index) + 1,
+        )
+    }
+}

src/strategy/mod.rs

@@ -1,10 +1,12 @@
 pub mod base;
 
+pub mod box_line;
 pub mod hidden_single;
 pub mod naked_single;
 
 pub use base::Strategy;
 pub use base::StrategyFn;
 
+pub use box_line::BoxLine;
 pub use hidden_single::HiddenSingle;
 pub use naked_single::NakedSingle;

src/strategy/naked_single.rs

@@ -1,4 +1,10 @@
-use crate::{board::Board, square::Square, strategy::Strategy};
+use std::fmt::{Display, Write};
+
+use crate::{
+    board::{index_to_col, index_to_row, Board},
+    square::Square,
+    strategy::Strategy,
+};
 
 pub struct NakedSingle {
     index: u8,
@@ -32,3 +38,15 @@ impl Strategy for NakedSingle {
         board
     }
 }
+
+impl Display for NakedSingle {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "Naked Single {} at row {} col {}",
+            self.value,
+            index_to_row(self.index) + 1,
+            index_to_col(self.index) + 1,
+        )
+    }
+}