naked pair

src/bin/example/main.rs

@@ -7,7 +7,8 @@ use sudoku::{
         puzzle::SudokuPuzzle,
         techniques::{
             hidden_pair_blk, hidden_pair_col, hidden_pair_row, hidden_single_blk,
-            hidden_single_col, hidden_single_row, naked_single,
+            hidden_single_col, hidden_single_row, naked_pair_blk, naked_pair_col, naked_pair_row,
+            naked_single,
         },
     },
     ui::{draw_grid, draw_numbers},
@@ -39,12 +40,18 @@ fn main() -> io::Result<()> {
     let res_hidden_pair_row = hidden_pair_row(&puzzle);
     let res_hidden_pair_col = hidden_pair_col(&puzzle);
     let res_hidden_pair_blk = hidden_pair_blk(&puzzle);
+    let res_naked_pair_row = naked_pair_row(&puzzle);
+    let res_naked_pair_col = naked_pair_col(&puzzle);
+    let res_naked_pair_blk = naked_pair_blk(&puzzle);
     println!("hidden single in row: {:?}", res_hidden_single_row);
     println!("hidden single in col: {:?}", res_hidden_single_col);
     println!("hidden single in blk: {:?}", res_hidden_single_blk);
     println!("naked single: {:?}", res_naked_single);
     println!("hidden pair in row: {:?}", res_hidden_pair_row);
     println!("hidden pair in col: {:?}", res_hidden_pair_col);
     println!("hidden pair in blk: {:?}", res_hidden_pair_blk);
+    println!("naked pair in row: {:?}", res_naked_pair_row);
+    println!("naked pair in col: {:?}", res_naked_pair_col);
+    println!("naked pair in blk: {:?}", res_naked_pair_blk);
     Ok(())
 }

src/neo/techniques.rs

@@ -139,3 +139,56 @@ pub fn hidden_pair_blk(
         block_idx_2_coord,
     )
 }
+
+fn naked_pair<T, F>(
+    puzzle: &T,
+    coord_transform: F,
+) -> Option<((usize, usize), (usize, usize), i8, i8)>
+where
+    T: Grid + TrackingCandidates,
+    F: Fn(usize, usize) -> (usize, usize),
+{
+    for i in 0..9 {
+        let js: Vec<usize> = (0..9)
+            .filter(|j| {
+                let (r, c) = coord_transform(i, *j);
+                puzzle.is_grid_empty(r, c) && puzzle.candidate_cnt_for_grid(r, c) == 2
+            })
+            .collect();
+        for i1 in 0..js.len() {
+            for i2 in 0..i1 {
+                let j1 = js[i1];
+                let j2 = js[i2];
+                let (r1, c1) = coord_transform(i, j1);
+                let (r2, c2) = coord_transform(i, j2);
+                if (1..=9).all(|num| {
+                    puzzle.is_candidate_of(r1, c1, num) == puzzle.is_candidate_of(r2, c2, num)
+                }) {
+                    let mut num_iter = (1..=9).filter(|num| puzzle.is_candidate_of(r1, c1, *num));
+                    let num1 = num_iter.next().unwrap();
+                    let num2 = num_iter.next().unwrap();
+                    return Some(((r1, c1), (r2, c2), num1, num2));
+                }
+            }
+        }
+    }
+    None
+}
+
+pub fn naked_pair_row(
+    puzzle: &(impl Grid + TrackingCandidates),
+) -> Option<((usize, usize), (usize, usize), i8, i8)> {
+    naked_pair(puzzle, |r, c| (r, c))
+}
+
+pub fn naked_pair_col(
+    puzzle: &(impl Grid + TrackingCandidates),
+) -> Option<((usize, usize), (usize, usize), i8, i8)> {
+    naked_pair(puzzle, |c, r| (r, c))
+}
+
+pub fn naked_pair_blk(
+    puzzle: &(impl Grid + TrackingCandidates),
+) -> Option<((usize, usize), (usize, usize), i8, i8)> {
+    naked_pair(puzzle, block_idx_2_coord)
+}