97 lines
2.1 KiB
Rust
97 lines
2.1 KiB
Rust
use std::collections::HashSet;
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type Index = i16;
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fn remvove_literal(cnf: &mut Vec<Vec<Index>>, l: Index) {
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cnf.retain(|c| c.binary_search(&l).is_err());
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for c in cnf {
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if let Ok(i) = c.binary_search(&(-l)) {
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c.remove(i);
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}
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}
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}
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fn unit_propagate(cnf: &mut Vec<Vec<Index>>, solution: &mut Vec<Index>) {
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if let Some(i) = cnf
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.iter()
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.rev()
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.position(|c| c.len() == 1)
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.map(|i| cnf.len() - i - 1)
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{
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let l = cnf[i][0];
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solution.push(l);
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cnf.swap_remove(i);
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remvove_literal(cnf, l);
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unit_propagate(cnf, solution);
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}
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}
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fn pure_literal_assign(cnf: &mut Vec<Vec<Index>>, solution: &mut Vec<Index>) {
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let mut literals: HashSet<Index> = HashSet::new();
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for c in cnf.iter() {
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literals.extend(c.iter());
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}
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for &l in &literals {
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if !literals.contains(&(-l)) {
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solution.push(l);
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remvove_literal(cnf, l);
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}
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}
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}
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pub fn dpll(cnf: &[Vec<Index>], solution: &mut Vec<Index>) -> bool {
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let prev_solution = solution.len();
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let mut own_cnf = cnf.to_owned();
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unit_propagate(&mut own_cnf, solution);
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pure_literal_assign(&mut own_cnf, solution);
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if own_cnf.is_empty() {
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return true;
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}
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if own_cnf.iter().any(|c| c.is_empty()) {
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solution.resize(prev_solution, 0);
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return false;
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}
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let literal = own_cnf[0][0];
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own_cnf.push(vec![literal]);
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if dpll(&own_cnf, solution) {
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return true;
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}
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own_cnf.last_mut().unwrap()[0] = -literal;
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if dpll(&own_cnf, solution) {
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return true;
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}
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solution.resize(prev_solution, 0);
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false
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}
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#[cfg(test)]
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mod test {
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use super::dpll;
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#[test]
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fn wikipedia() {
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let cnf = vec![
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vec![-1, 2, 3],
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vec![1, 3, 4],
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vec![-4, 1, 3],
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vec![-3, 1, 4],
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vec![-4, -3, 1],
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vec![-3, -2, 4],
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vec![-3, -1, 2],
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vec![-2, -1, 3],
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];
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let mut solution = Vec::new();
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assert!(dpll(&cnf, &mut solution));
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}
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}
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