day 10 part 2 progress!

almost there, just 2 stubborn instances that we can't solve and i think i
know why.

day10/sol2.go

@@ -2,8 +2,10 @@ package main
 
 import (
 	"bufio"
+	"container/heap"
 	"fmt"
 	"log"
+	"math/bits"
 	"os"
 	"strconv"
 	"strings"
@@ -39,6 +41,7 @@ func solve(filename string) {
 	scanner := bufio.NewScanner(input)
 	scanner.Split(bufio.ScanLines)
 	total := 0
+	errors := 0
 	for scanner.Scan() {
 		line := scanner.Text()
 		parts := strings.Fields(line)
@@ -57,11 +60,19 @@ func solve(filename string) {
 		fmt.Printf("%v %b %v\n", target, buts, parts)
 		n := solveJolts(target, buts)
 		fmt.Printf("%s = %v\n", line, n)
+		fmt.Println()
+		if n >= 0 {
 			total += n
+		} else {
+			errors += 1
+		}
 		//fmt.Println(n)
 	}
 	check(scanner.Err())
 	fmt.Println(total)
+	if errors > 0 {
+		fmt.Printf("error! failed to solve %d instances\n", errors)
+	}
 
 }
 
@@ -111,15 +122,19 @@ func (j *Jolts) uint32() (u uint32) {
 	return u
 }
 
-func (j Jolts) Sub(m uint32, value int) Jolts {
+func (j Jolts) Add(m uint32, value int) Jolts {
 	for i := range j {
 		if m>>i&1 != 0 {
-			j[i] -= int16(value)
+			j[i] += int16(value)
 		}
 	}
 	return j
 }
 
+func (j Jolts) Sub(m uint32, value int) Jolts {
+	return j.Add(m, -value)
+}
+
 func (j Jolts) Valid() bool {
 	for i := range j {
 		if j[i] < 0 {
@@ -129,6 +144,31 @@ func (j Jolts) Valid() bool {
 	return true
 }
 
+func (j Jolts) Less(k Jolts) bool {
+	for i := range j {
+		if j[i] != k[i] {
+			return j[i] < k[i]
+		}
+	}
+	return false // equal
+}
+
+func (j Jolts) BitLength() int {
+	var total uint32
+	for _, x := range j {
+		total |= uint32(x)
+	}
+	return bits.Len32(total)
+}
+
+func (j Jolts) BitSlice(bit int) uint32 {
+	var mask uint32
+	for i, x := range j {
+		mask |= (uint32(x) >> uint(bit)) & 1 << uint(i)
+	}
+	return mask
+}
+
 // TODO: this isn't quite enough. we need to know not only how many button presses
 // a mask can be solved in, but also *the specific buttons* -- because even though
 // each button is pressed at most once, two buttons can be connected to the same
@@ -140,24 +180,68 @@ func (j Jolts) Valid() bool {
 // since it depends only on the button wiring. all that's left after that is a
 // graph search through the state space, using masks to prune each level.
 
+// suppose we have four buttons whose bitmasks are 110, 101, 011, and 100.
+// suppose our target jolts are [2 1 1], corresponding to bitmasks 100x2 and 011x1.
+// the shortest solution for the low bits (011) is to press button 3 once. but then we need
+// to press button 4 twice to get the 2nd bits. that's 3 total button presses.
+// a more efficient solution is to press button 1 once and button 2 once (110+101 = 211),
+// for 2 total button presses.
+// this is a potential issue whenever we have a set of buttons which aren't linearly independent
+// (e.g. button 1 ^ 2 ^ 3 = button 4). we know this to be the case in some of the inputs.
+
 func solveJolts(target Jolts, pool []uint32) int {
-	var bits uint32
+	var bitcost = new(state)
-	for _, x := range target {
+	bitcost.init(pool)
-		bits |= uint32(x)
+	for mask, vals := range bitcost.nodes {
-	}
+		fmt.Printf("%b: %v\n", mask, vals)
-	var answer int
-	for bit := uint(0); bits>>bit > 0; bit++ {
-		var mask uint32
-		for i := range target {
-			mask |= uint32(target[i]) >> bit << i
 	}
 
+	bits := target.BitLength()
+
+	qu := newHeap(target)
+	var zero Jolts
+	addstates := func(t, n Node, bit int) Node {
+		t.cost += n.cost << bit
+		t.mask += 1
+		for i := range t.jolts {
+			t.jolts[i] -= n.jolts[i] << bit
+		}
+		return t
+	}
+	ntargets := len(target)
+	for ntargets > 1 && target[ntargets-1] == 0 {
+		ntargets--
+	}
+	seen := make(map[Jolts]bool)
+	for qu.Len() > 0 {
+		this := heap.Pop(qu).(Node)
+		log.Printf("sj: %v, len(q) = %v", this, qu.Len()+1)
+		if this.jolts == zero {
+			return int(this.cost)
+		}
+		seen[this.jolts] = true
+
+		bit := int(this.mask)
+		if bit >= int(bits) {
+			continue
+		}
+		//mask := masks[this.mask]
+		mask := this.jolts.BitSlice(bit)
+		log.Printf("jolts = %v, bit = %d, mask = %0*b", this.jolts, bit, ntargets, mask)
+
 		if mask == 0 {
+			seen[this.jolts] = false
+			this.mask += 1
+			qu.AddNode(this)
 			continue
 		}
 
-		n := best(mask, pool)
+		for _, n := range bitcost.best(mask) {
-		answer += n << bit
+			t := addstates(this, n, int(bit))
+			if t.jolts.Valid() && !seen[t.jolts] {
+				qu.AddNode(t)
+			}
+		}
 
 		//for i, p := range pool {
 		//	if mask>>i&1 != 0 {
@@ -165,29 +249,120 @@ func solveJolts(target Jolts, pool []uint32) int {
 		//	}
 		//}
 	}
-	return answer
+	log.Printf("%v: no solution found\n", target)
+	return -1
 }
 
-func best(target uint32, pool []uint32) int {
+type Node struct {
-	var cost = make(map[uint32]int)
+	mask    uint32
-	var states = []uint32{0}
+	buttons uint32
-	cost[0] = 0
+	cost    int32
-	for _, p := range pool {
+	jolts   Jolts
-		// enumerate all the states that can be reached by toggling button p
+}
-		for _, s := range states {
-			t := s ^ p
-			c := cost[t] + 1
 
-			if cost_t, ok := cost[t]; ok {
+func (n Node) Add(mask uint32) Node {
-				if c < cost_t {
+	n.mask ^= mask
-					cost[t] = c
+	n.cost += 1
+	n.jolts = n.jolts.Add(mask, 1)
+	return n
+}
+
+//func (n *Node) cost() int { return bits.OnesCount(n.buttons) }
+
+type Heap struct {
+	heap []Node
+	idx  map[Jolts]int
+}
+
+// these functions are for the heap.Interface interface
+// start
+
+func (h *Heap) Len() int { return len(h.heap) }
+
+func (h *Heap) Less(i, j int) bool {
+	if h.heap[i].cost != h.heap[j].cost {
+		return h.heap[i].cost < h.heap[j].cost
+	}
+	return h.heap[i].jolts.Less(h.heap[j].jolts)
+}
+
+func (h *Heap) Swap(i, j int) {
+	h.heap[i], h.heap[j] = h.heap[j], h.heap[i]
+	h.idx[h.heap[i].jolts] = i
+	h.idx[h.heap[j].jolts] = j
+}
+
+func (h *Heap) Push(x any) {
+	n := x.(Node)
+	h.heap = append(h.heap, n)
+	h.idx[n.jolts] = len(h.heap) - 1
+}
+
+func (h *Heap) Pop() any {
+	old := h.heap
+	n := len(old)
+	x := old[n-1]
+	h.heap = old[0 : n-1]
+	delete(h.idx, x.jolts)
+	return x
+}
+
+// end
+
+func (h *Heap) AddNode(t Node) {
+	defer func() {
+		if e := recover(); e != nil {
+			log.Println(h.heap)
+			log.Println(h.idx)
+			panic(e)
+		}
+	}()
+	if i, ok := h.idx[t.jolts]; ok {
+		old_cost := h.heap[i].cost
+		if t.cost < old_cost {
+			h.heap[i].cost = t.cost
+			heap.Fix(h, i)
+		} else {
+			// nothing; don't add node with higher cost to the queue
 		}
 	} else {
-				cost[t] = c
+		heap.Push(h, t)
-				states = append(states, t)
-			}
 	}
 }
 
-	return cost[target]
+func newHeap(start Jolts) *Heap {
+	var idx = make(map[Jolts]int)
+	idx[start] = 0
+	return &Heap{[]Node{{jolts: start}}, idx}
+}
+
+type state struct {
+	nodes map[uint32][]Node
+}
+
+func (s *state) init(pool []uint32) {
+	qu := newHeap(Jolts{})
+	best := make(map[uint32][]Node)
+	seen := make(map[uint32]bool)
+	for qu.Len() > 0 {
+		s := heap.Pop(qu).(Node)
+		best[s.mask] = append(best[s.mask], s)
+		// enumerate all the states that can be reached by toggling button p
+		for b, p := range pool {
+			if s.buttons>>b&1 == 0 {
+				t := s.Add(p)
+				t.buttons |= uint32(1) << b
+				if !seen[t.buttons] {
+					heap.Push(qu, t)
+					seen[t.buttons] = true
+				}
+				//qu.AddNode(t)
+			}
+		}
+	}
+	s.nodes = best
+}
+
+func (s *state) best(target uint32) []Node {
+	return s.nodes[target]
 }