2 files changed, 81 insertions(+), 40 deletions(-)

M aoc_2022/day14/day14.go
M aoc_2022/test.exp

@@ 2,38 2,13 @@ package day14
 
 import (
 	"bufio"
-	"container/heap"
-	//	"fmt"
 	"os"
+	"sort"
 	"strconv"
 	"strings"
 	"williewillus/aoc_2022/util"
 )
 
-// cargo culted from container/heap doc
-// An IntHeap is a min-heap of ints.
-type IntHeap []int
-
-func (h IntHeap) Len() int           { return len(h) }
-func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }
-func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
-
-func (h *IntHeap) Push(x interface{}) {
-	// Push and Pop use pointer receivers because they modify the slice's length,
-	// not just its contents.
-	*h = append(*h, x.(int))
-}
-
-func (h *IntHeap) Pop() interface{} {
-	old := *h
-	n := len(old)
-	x := old[n-1]
-	*h = old[0 : n-1]
-	return x
-}
-
-// End cargo cult
-
 type vec2 util.Vec2
 
 func parse(s string) (int, int) {


@@ 57,10 32,72 @@ func iorder(a, b int) (int, int) {
 	}
 }
 
+const spawnX int = 500
+const spawnY int = 0
+
+func posOccupied(state map[int][]int, pos vec2) bool {
+	col, ok := state[pos.X]
+	if !ok {
+		return false
+	}
+	idx := sort.SearchInts(col, pos.Y)
+	return idx < len(col) && col[idx] == pos.Y
+}
+
+// Get the next occupied y coordinate "below" (greater than) the given x, y coordinate.
+// Returns -1 if one doesn't exist
+func getNextOccupiedBelow(state map[int][]int, pos vec2) int {
+	col, ok := state[pos.X]
+	if !ok {
+		return -1
+	}
+	nextYIdx := sort.Search(len(col), func(idx int) bool {
+		return col[idx] > pos.Y
+	})
+	
+	if nextYIdx < len(col) {
+		return col[nextYIdx]
+	} else {
+		return -1
+	}
+}
+
+// Spawn a sand at spawnX, spawnY and simulate it until it comes to rest
+// Second return value is false if the particle falls off the board, vec2 holds the last known step before falling off
+// if it's true, then vec2 is the place it came to rest
+func simulateNextSand(state map[int][]int) (vec2, bool) {
+	pos := vec2{spawnX, spawnY}
+	for {
+		// Try moving down
+		nextOccupied := getNextOccupiedBelow(state, pos)
+		if nextOccupied == -1 {
+			return pos, false
+		}
+
+		toMoveDownTo := vec2{pos.X, nextOccupied - 1}
+
+		if toMoveDownTo == pos {
+			// Already as far down as we can go, try moving sideways
+			downLeft := vec2{pos.X-1, pos.Y + 1}
+			downRight := vec2{pos.X+1, pos.Y + 1}
+			if !posOccupied(state, downLeft) {
+				pos = downLeft
+			} else if !posOccupied(state, downRight) {
+				pos = downRight
+			} else {
+				// Nowhere to go, come to rest
+				return pos, true
+			}
+		} else {
+			pos = toMoveDownTo
+		}
+	}
+}
+
 func Run() (string, string) {
 	scanner := bufio.NewScanner(os.Stdin)
-	// x -> heap of filled y's
-	state := make(map[int]*IntHeap)
+	// x -> filled Y coords (sorted)
+	state := make(map[int][]int)
 	for scanner.Scan() {
 		line := scanner.Text()
 		points := []vec2{}


@@ 78,22 115,26 @@ func Run() (string, string) {
 
 			for x := startX; x <= endX; x++ {
 				for y := startY; y <= endY; y++ {
-					h, ok := state[x]
-					if !ok {
-						h = &IntHeap{}
-					}
-					heap.Push(h, y)
-					state[x] = h
+					state[x] = append(state[x], y)
 				}
 			}
 		}
 	}
 
-	/*
-		for x, ys := range state {
-			fmt.Printf("top at x=%d is y=%d\n", x, (*ys)[0])
+	for _, col := range state {
+		sort.Ints(col)
+	}
+
+	p1 := 0
+	for ; ; p1++ {
+		restPos, didRest := simulateNextSand(state)
+		if !didRest {
+			break
+		} else {
+			state[restPos.X] = append(state[restPos.X], restPos.Y)
+			sort.Ints(state[restPos.X])
 		}
-	*/
+	}	
 
-	return "incomplete", "incomplete"
+	return strconv.Itoa(p1), "incomplete"
 }

@@ 44,7 44,7 @@ Part 2: 386
 Part 1: 6272
 Part 2: 22288
 --> Running day 14
-Part 1: incomplete
+Part 1: 805
 Part 2: incomplete
 --> Running day 15
 Part 1: unimplemented