Initial commit.

internal/solver/bounded_tracking/bounded_tracking.go

@@ -0,0 +1,86 @@
+package bounded_tracking
+
+import (
+	"container/heap"
+
+	"smariot.com/tsp/internal/solver/problem"
+)
+
+type minHeap[P problem.Problem[State], State comparable] struct {
+	problem problem.Problem[State]
+	known   map[State]int
+	items   []State
+}
+
+func (h minHeap[P, State]) Len() int {
+	return len(h.items)
+}
+
+func (h minHeap[P, State]) Less(i, j int) bool {
+	return h.problem.OptimisticLess(h.items[i], h.items[j])
+}
+
+func (h minHeap[P, State]) Swap(i, j int) {
+	h.items[i], h.items[j] = h.items[j], h.items[i]
+	h.known[h.items[i]] = i
+	h.known[h.items[j]] = j
+}
+
+func (h *minHeap[P, State]) Push(x any) {
+	state := x.(State)
+	h.items = append(h.items, state)
+	h.known[state] = len(h.items)
+}
+
+func (h *minHeap[P, State]) Pop() any {
+	n := len(h.items)
+	state := h.items[n-1]
+	h.items = h.items[:n-1]
+	delete(h.known, state)
+	return state
+}
+
+type solver[P problem.Problem[State], State comparable] struct {
+	minHeap[P, State]
+}
+
+func (s *solver[P, State]) Push(state State) {
+	if i, ok := s.known[state]; ok {
+		// The state is already in the heap, update its position instead.
+		heap.Fix(&s.minHeap, i)
+		return
+	}
+
+	heap.Push(&s.minHeap, state)
+}
+
+func (s *solver[P, State]) Pop() (State, bool) {
+	if s.Len() == 0 {
+		var zero State
+		return zero, false
+	}
+
+	return heap.Pop(&s.minHeap).(State), true
+}
+
+func (s *solver[P, State]) Reset() {
+	for _, state := range s.items {
+		s.problem.Discard(state)
+	}
+
+	s.items = s.items[:0]
+	clear(s.known)
+}
+
+// Returns a solver that for bounded problems that can update their states.
+//
+// Submitting a state that is already in the heap will update its position,
+// rather than adding it again. problem.Discard will only be invoked once.
+func New[P problem.Problem[State], State comparable](problem P) *solver[P, State] {
+	return &solver[P, State]{
+		minHeap: minHeap[P, State]{
+			problem: problem,
+			known:   make(map[State]int),
+		},
+	}
+}