107 lines
2.7 KiB
Rust
107 lines
2.7 KiB
Rust
//! N-queens problem.
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//!
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//! https://en.wikipedia.org/wiki/Eight_queens_puzzle
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extern crate puzzle_solver;
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use puzzle_solver::*;
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use std::rc::Rc;
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#[derive(Debug)]
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struct NoDiagonal {
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vars: Vec<VarToken>,
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}
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impl Constraint for NoDiagonal {
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fn vars(&self) -> Box<dyn Iterator<Item = &'_ VarToken> + '_> {
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Box::new(self.vars.iter())
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}
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fn propagate(&self, search: &mut PuzzleSearch, var: VarToken, val: Val) -> PsResult<()> {
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let y1 = self
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.vars
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.iter()
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.position(|&v| v == var)
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.expect("unreachable");
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for (y2, &var2) in self.vars.iter().enumerate() {
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if !search.is_assigned(var2) {
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let x1 = val;
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let dy = (y1 as Val) - (y2 as Val);
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search.remove_candidate(var2, x1 - dy)?;
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search.remove_candidate(var2, x1 + dy)?;
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}
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}
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Ok(())
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}
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fn substitute(&self, _from: VarToken, _to: VarToken) -> PsResult<Rc<dyn Constraint>> {
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unimplemented!();
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}
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}
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fn make_queens(n: usize) -> (Puzzle, Vec<VarToken>) {
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let mut sys = Puzzle::new();
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let pos: Vec<Val> = (0..n as Val).collect();
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let vars = sys.new_vars_with_candidates_1d(n, &pos);
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sys.all_different(&vars);
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sys.add_constraint(NoDiagonal { vars: vars.clone() });
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(sys, vars)
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}
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fn print_queens(dict: &Solution, vars: &[VarToken]) {
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let n = vars.len() as Val;
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for &var in vars.iter() {
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for i in 0..n {
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print!(" {}", if i == dict[var] { "Q" } else { "." });
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}
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println!();
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}
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}
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#[test]
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fn queens_4x4() {
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let (mut sys, vars) = make_queens(4);
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let dict = sys.solve_all();
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assert_eq!(dict.len(), 2);
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print_queens(&dict[0], &vars);
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println!("queens_4x4: {} guesses", sys.num_guesses());
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}
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#[test]
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fn queens_5x5() {
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let (mut sys, vars) = make_queens(5);
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let dict = sys.solve_all();
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assert_eq!(dict.len(), 10);
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print_queens(&dict[0], &vars);
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println!("queens_5x5: {} guesses", sys.num_guesses());
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}
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#[test]
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fn queens_6x6() {
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let (mut sys, vars) = make_queens(6);
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let dict = sys.solve_all();
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assert_eq!(dict.len(), 4);
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print_queens(&dict[0], &vars);
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println!("queens_6x6: {} guesses", sys.num_guesses());
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}
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#[test]
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fn queens_7x7() {
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let (mut sys, vars) = make_queens(7);
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let dict = sys.solve_all();
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assert_eq!(dict.len(), 40);
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print_queens(&dict[0], &vars);
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println!("queens_7x7: {} guesses", sys.num_guesses());
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}
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#[test]
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fn queens_8x8() {
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let (mut sys, vars) = make_queens(8);
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let dict = sys.solve_all();
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assert_eq!(dict.len(), 92);
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print_queens(&dict[0], &vars);
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println!("queens_8x8: {} guesses", sys.num_guesses());
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}
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