replace nested loop with `.find`

rust/solve/src/dpll.rs

@@ -153,15 +153,9 @@ pub fn dpll(clauses: Vec<Clause>) -> Option<BoundVars> {
        } else { // none of the above, decide (guess) an unknown variable
            let mut unknown: Var = 0;
            for c in clauses.clone() {
                for v in c {
                    if is_unknown(vars, v) {
                        unknown = v;
                        break;
                    }
                }
                
                if unknown != 0 {
                    break;
                match c.iter().find(|&v| is_unknown(vars, *v)) {
                    Some(&u) => { unknown = u; break }
                    None => continue
                }
            }
            assert!(unknown != 0);