Implement 'twosat'

Author: manta1130

src/lib.rs

@@ -31,3 +31,4 @@ pub use string::{
     lcp_array, lcp_array_arbitrary, suffix_array, suffix_array_arbitrary, suffix_array_manual,
     z_algorithm, z_algorithm_arbitrary,
 };
+pub use twosat::TwoSAT;

src/twosat.rs

@@ -1 +1,36 @@
+use crate::internal_scc;
 
+pub struct TwoSAT {
+    n: usize,
+    scc: internal_scc::SccGraph,
+    answer: Vec<bool>,
+}
+impl TwoSAT {
+    pub fn new(n: usize) -> Self {
+        TwoSAT {
+            n,
+            answer: vec![false; n],
+            scc: internal_scc::SccGraph::new(2 * n),
+        }
+    }
+    pub fn add_clause(&mut self, i: usize, f: bool, j: usize, g: bool) {
+        assert!(i < self.n && j < self.n);
+        self.scc
+            .add_edge(2 * i + if f { 0 } else { 1 }, 2 * j + if g { 1 } else { 0 });
+        self.scc
+            .add_edge(2 * j + if f { 0 } else { 1 }, 2 * i + if g { 1 } else { 0 });
+    }
+    pub fn satisfiable(&mut self) -> bool {
+        let id = self.scc.scc_ids().1;
+        for i in 0..self.n {
+            if id[2 * i] == id[2 * i + 1] {
+                return false;
+            }
+            self.answer[i] = id[2 * i] < id[2 * i + 1];
+        }
+        true
+    }
+    pub fn answer(&self) -> &Vec<bool> {
+        &self.answer
+    }
+}