update vendor

vendor/github.com/crillab/gophersat/explain/problem.go

@@ -0,0 +1,125 @@
+package explain
+
+import (
+	"fmt"
+	"strings"
+)
+
+// A Problem is a conjunction of Clauses.
+// This package does not use solver's representation.
+// We want this code to be as simple as possible to be easy to audit.
+// On the other hand, solver's code must be as efficient as possible.
+type Problem struct {
+	Clauses   [][]int
+	NbVars    int
+	NbClauses int
+	units     []int // For each var, 0 if the var is unbound, 1 if true, -1 if false
+	Options   Options
+	tagged    []bool // List of claused used whil proving the problem is unsat. Initialized lazily
+}
+
+func (pb *Problem) initTagged() {
+	pb.tagged = make([]bool, pb.NbClauses)
+	for i, clause := range pb.Clauses {
+		// Unit clauses are tagged as they will probably be used during resolution
+		pb.tagged[i] = len(clause) == 1
+	}
+}
+
+func (pb *Problem) clone() *Problem {
+	pb2 := &Problem{
+		Clauses:   make([][]int, pb.NbClauses),
+		NbVars:    pb.NbVars,
+		NbClauses: pb.NbClauses,
+		units:     make([]int, pb.NbVars),
+	}
+	copy(pb2.units, pb.units)
+	for i, clause := range pb.Clauses {
+		pb2.Clauses[i] = make([]int, len(clause))
+		copy(pb2.Clauses[i], clause)
+	}
+	return pb2
+}
+
+// restore removes all learned clauses, if any.
+func (pb *Problem) restore() {
+	pb.Clauses = pb.Clauses[:pb.NbClauses]
+}
+
+// unsat will be true iff the problem can be proven unsat through unit propagation.
+// This methods modifies pb.units.
+func (pb *Problem) unsat() bool {
+	done := make([]bool, len(pb.Clauses)) // clauses that were deemed sat during propagation
+	modified := true
+	for modified {
+		modified = false
+		for i, clause := range pb.Clauses {
+			if done[i] { // That clause was already proved true
+				continue
+			}
+			unbound := 0
+			var unit int // An unbound literal, if any
+			sat := false
+			for _, lit := range clause {
+				v := lit
+				if v < 0 {
+					v = -v
+				}
+				binding := pb.units[v-1]
+				if binding == 0 {
+					unbound++
+					if unbound == 1 {
+						unit = lit
+					} else {
+						break
+					}
+				} else if binding*lit == v { // (binding == -1 && lit < 0) || (binding == 1 && lit > 0) {
+					sat = true
+					break
+				}
+			}
+			if sat {
+				done[i] = true
+				continue
+			}
+			if unbound == 0 {
+				// All lits are false: problem is UNSAT
+				if i < pb.NbClauses {
+					pb.tagged[i] = true
+				}
+				return true
+			}
+			if unbound == 1 {
+				if unit < 0 {
+					pb.units[-unit-1] = -1
+				} else {
+					pb.units[unit-1] = 1
+				}
+				done[i] = true
+				if i < pb.NbClauses {
+					pb.tagged[i] = true
+				}
+				modified = true
+			}
+		}
+	}
+	// Problem is either sat or could not be proven unsat through unit propagation
+	return false
+}
+
+// CNF returns a representation of the problem using the Dimacs syntax.
+func (pb *Problem) CNF() string {
+	lines := make([]string, 1, pb.NbClauses+1)
+	lines[0] = fmt.Sprintf("p cnf %d %d", pb.NbVars, pb.NbClauses)
+	for i := 0; i < pb.NbClauses; i++ {
+		clause := pb.Clauses[i]
+		strClause := make([]string, len(clause)+1)
+		for i, lit := range clause {
+			strClause[i] = fmt.Sprintf("%d", lit)
+		}
+		strClause[len(clause)] = "0"
+		line := strings.Join(strClause, " ")
+		lines = append(lines, line)
+	}
+	return strings.Join(lines, "\n")
+}