diff --git a/solutions/alessio/day21/aoc21 b/solutions/alessio/day21/aoc21
new file mode 100755
index 0000000..b52e4c1
Binary files /dev/null and b/solutions/alessio/day21/aoc21 differ
diff --git a/solutions/alessio/day21/day21.go b/solutions/alessio/day21/day21.go
new file mode 100644
index 0000000..fcb5d69
--- /dev/null
+++ b/solutions/alessio/day21/day21.go
@@ -0,0 +1,174 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func check(e error) {
+	if e != nil {
+		panic(e)
+	}
+}
+
+type Pos struct {
+	r, c int
+}
+
+var dirSymbols map[Pos]string = map[Pos]string{
+	{0, 1}:  ">",
+	{0, -1}: "<",
+	{1, 0}:  "v",
+	{-1, 0}: "^",
+}
+
+type PosPath struct {
+	pos  Pos
+	path string
+}
+
+var numPad map[byte]Pos = map[byte]Pos{
+	'7': {0, 0},
+	'8': {0, 1},
+	'9': {0, 2},
+	'4': {1, 0},
+	'5': {1, 1},
+	'6': {1, 2},
+	'1': {2, 0},
+	'2': {2, 1},
+	'3': {2, 2},
+	'-': {3, 0},
+	'0': {3, 1},
+	'A': {3, 2},
+}
+
+var dirPad map[byte]Pos = map[byte]Pos{
+	'-': {0, 0},
+	'^': {0, 1},
+	'A': {0, 2},
+	'<': {1, 0},
+	'v': {1, 1},
+	'>': {1, 2},
+}
+
+func getNextDirs(from Pos, to Pos) []Pos {
+	nextDirs := []Pos{}
+	if to.r > from.r {
+		nextDirs = append(nextDirs, Pos{1, 0})
+	}
+	if to.r < from.r {
+		nextDirs = append(nextDirs, Pos{-1, 0})
+	}
+	if to.c > from.c {
+		nextDirs = append(nextDirs, Pos{0, 1})
+	}
+	if to.c < from.c {
+		nextDirs = append(nextDirs, Pos{0, -1})
+	}
+	return nextDirs
+}
+
+func getPadPaths(start byte, end byte, byteToPos map[byte]Pos) []string {
+	posToByte := map[Pos]byte{}
+	for k, v := range byteToPos {
+		posToByte[v] = k
+	}
+	paths := []string{}
+	startPosPath := PosPath{byteToPos[start], ""}
+	q := []PosPath{startPosPath}
+	for len(q) > 0 {
+		curr := q[0]
+		q = q[1:]
+
+		if curr.pos == byteToPos[end] {
+			paths = append(paths, curr.path+"A")
+			continue
+		}
+
+		for _, dir := range getNextDirs(curr.pos, byteToPos[end]) {
+			nextPos := Pos{curr.pos.r + dir.r, curr.pos.c + dir.c}
+			dirSym := dirSymbols[dir]
+			path := curr.path + dirSym
+			nextPosPath := PosPath{nextPos, path}
+			if posToByte[nextPos] != '-' && posToByte[nextPos] != start {
+				q = append(q, nextPosPath)
+			}
+		}
+	}
+	return paths
+}
+
+type MemoKey struct {
+	path string
+	lvl  int
+}
+
+func getShortestPath(seq string, lvl int, maxLvl int, memo *map[MemoKey]int, useNumPad bool) int {
+	if lvl == maxLvl {
+		return len(seq)
+	}
+
+	if val, ok := (*memo)[MemoKey{seq, lvl}]; ok {
+		return val
+	}
+
+	start := 'A'
+	totMinLen := 0
+	pad := dirPad
+	if useNumPad {
+		pad = numPad
+	}
+	for _, c := range seq {
+		paths := getPadPaths(byte(start), byte(c), pad)
+		min := math.MaxInt
+		for _, p := range paths {
+			l := getShortestPath(p, lvl+1, maxLvl, memo, false)
+			if l < min {
+				min = l
+			}
+		}
+		totMinLen += min
+		start = c
+	}
+	(*memo)[MemoKey{seq, lvl}] = totMinLen
+	return totMinLen
+}
+
+func solve(lines []string, levels int) {
+	sum := 0
+	memo := map[MemoKey]int{}
+	for _, l := range lines {
+		totMinLen := getShortestPath(l, -1, levels, &memo, true)
+		numPart, _ := strconv.Atoi(l[:len(l)-1])
+		fmt.Printf("%d * %d\n", totMinLen, numPart)
+		sum += totMinLen * numPart
+	}
+
+	fmt.Println(sum)
+}
+
+func part1(lines []string) {
+	solve(lines, 2)
+}
+
+func part2(lines []string) {
+	solve(lines, 25)
+}
+
+func main() {
+	data, err := os.ReadFile("./input21_def.txt")
+	check(err)
+	dataStr := strings.ReplaceAll(string(data), "\r\n", "\n")
+	lines := strings.Split(strings.Trim(dataStr, "\n"), "\n")
+
+	start := time.Now()
+	part1(lines)
+	fmt.Printf("part1: %s\n", time.Since(start))
+	start = time.Now()
+	part2(lines)
+	fmt.Printf("part2: %s\n", time.Since(start))
+}
diff --git a/solutions/alessio/day21/go.mod b/solutions/alessio/day21/go.mod
new file mode 100644
index 0000000..89ebaba
--- /dev/null
+++ b/solutions/alessio/day21/go.mod
@@ -0,0 +1,10 @@
+module aoc21
+
+go 1.23
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/testify v1.10.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/solutions/alessio/day21/go.sum b/solutions/alessio/day21/go.sum
new file mode 100644
index 0000000..fe99d71
--- /dev/null
+++ b/solutions/alessio/day21/go.sum
@@ -0,0 +1,9 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
+github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/solutions/alessio/day21/graph/graph.go b/solutions/alessio/day21/graph/graph.go
new file mode 100644
index 0000000..51cb573
--- /dev/null
+++ b/solutions/alessio/day21/graph/graph.go
@@ -0,0 +1,197 @@
+package graph
+
+import (
+	"fmt"
+	"math"
+	"slices"
+)
+
+type Graph[T comparable] struct {
+	Nodes   []Node[T]
+	Edges   []Edge[T]
+	AdjList map[T][]Edge[T]
+}
+
+type Node[T any] struct {
+	Val T
+}
+
+type Edge[T any] struct {
+	Weight int
+	From   T
+	To     *Node[T]
+}
+
+func (graph *Graph[T]) AddNode(val T) *Node[T] {
+	node := Node[T]{Val: val}
+	graph.Nodes = append(graph.Nodes, node)
+	return &node
+}
+
+func (graph *Graph[T]) RemoveNode(val T) {
+	delete(graph.AdjList, val)
+	for i, lst := range graph.AdjList {
+		idx := -1
+		for j, e := range lst {
+			if e.To.Val == val {
+				idx = j
+				break
+			}
+		}
+		if idx != -1 {
+			graph.AdjList[i] = slices.Concat(lst[:idx], lst[idx+1:])
+		}
+	}
+}
+
+func (graph *Graph[T]) AddEdge(from T, to T, weight int) *Edge[T] {
+	toNode := graph.GetNode(to)
+	if toNode == nil {
+		fmt.Println("Error: toNode is nil")
+		return nil
+	}
+	edge := Edge[T]{Weight: weight, To: toNode}
+	graph.Edges = append(graph.Edges, edge)
+	graph.AdjList[from] = append(graph.AdjList[from], edge)
+	return &edge
+}
+
+func (graph *Graph[T]) AddUndirectedEdge(from T, to T, weight int) {
+	graph.AddEdge(from, to, weight)
+	graph.AddEdge(to, from, weight)
+}
+
+func (graph *Graph[T]) HasNode(val T) bool {
+	return slices.ContainsFunc(graph.Nodes, func(n Node[T]) bool { return n.Val == val })
+}
+
+func (graph *Graph[T]) HasEdge(from T, to T) bool {
+	for _, e := range graph.AdjList[from] {
+		if e.To.Val == to {
+			return true
+		}
+	}
+	return false
+}
+
+func (graph *Graph[T]) GetNode(val T) *Node[T] {
+	for _, n := range graph.Nodes {
+		if n.Val == val {
+			return &n
+		}
+	}
+	return nil
+}
+
+func (graph *Graph[T]) Init(nodes int, edges int) {
+	graph.Nodes = make([]Node[T], 0, nodes)
+	graph.Edges = make([]Edge[T], 0, edges)
+	graph.AdjList = make(map[T][]Edge[T], nodes)
+}
+
+func (graph *Graph[T]) ShortestPath(from T, to T) (int, map[T]bool, []T) {
+	start := graph.GetNode(from)
+	end := graph.GetNode(to)
+	dist := make(map[T]int, len(graph.Nodes))
+	path := map[T]bool{}
+	orderedPath := []T{}
+	nodes := make([]T, 0, len(graph.Nodes))
+	for _, n := range graph.Nodes {
+		dist[n.Val] = math.MaxInt
+		nodes = append(nodes, n.Val)
+	}
+
+	dist[start.Val] = 0
+	for len(path) < len(nodes) {
+		curr := graph.getClosest(nodes, dist, path)
+		if path[curr] {
+			continue
+		}
+
+		path[curr] = true
+		orderedPath = append(orderedPath, curr)
+
+		if curr == end.Val {
+			break
+		}
+
+		for _, e := range graph.AdjList[curr] {
+			// relaxation on the edge
+			if !path[e.To.Val] && dist[curr]+e.Weight < dist[e.To.Val] {
+				dist[e.To.Val] = dist[curr] + e.Weight
+			}
+		}
+	}
+	return dist[end.Val], path, orderedPath
+}
+
+func (graph *Graph[T]) GetOnlyPath(from T, to T) (map[T]bool, []T) {
+	start := graph.GetNode(from)
+	end := graph.GetNode(to)
+	path := map[T]bool{}
+	orderedPath := []T{}
+
+	curr := start.Val
+	for curr != end.Val {
+		path[curr] = true
+		orderedPath = append(orderedPath, curr)
+		numAdj := len(graph.AdjList[curr])
+		if numAdj > 2 {
+			panic("too many adjacents")
+		}
+		for _, e := range graph.AdjList[curr] {
+			if !path[e.To.Val] {
+				curr = e.To.Val
+				break
+			}
+		}
+	}
+	path[curr] = true
+	orderedPath = append(orderedPath, curr)
+	return path, orderedPath
+}
+
+func (graph *Graph[T]) getClosest(nodes []T, dist map[T]int, visited map[T]bool) T {
+	var minNode T
+	minDist := math.MaxInt
+
+	for _, n := range nodes {
+		if !visited[n] && dist[n] <= minDist {
+			minDist = dist[n]
+			minNode = n
+		}
+	}
+	return minNode
+}
+
+func (graph *Graph[T]) GetFullPathsEdges(start T, end T) []Edge[T] {
+	allEdges := []Edge[T]{}
+	min := math.MaxInt
+	graph.getBestPathsRec(start, &map[T]bool{}, []Edge[T]{}, &allEdges, end, 0, &min)
+	return allEdges
+}
+
+func (graph *Graph[T]) getBestPathsRec(currNode T, visited *map[T]bool, currPath []Edge[T], edges *[]Edge[T], end T, currVal int, currMin *int) {
+	if currNode == end {
+		fmt.Println("found path")
+		if currVal < *currMin {
+			*currMin = currVal
+			(*edges) = append([]Edge[T]{}, currPath...) // replace all
+		} else if currVal == *currMin {
+			(*edges) = append((*edges), currPath...)
+		}
+		return
+	}
+
+	(*visited)[currNode] = true
+	for _, e := range graph.AdjList[currNode] {
+		next := e.To.Val
+		if !(*visited)[next] {
+			e.From = currNode
+			if currVal+e.Weight <= *currMin {
+				graph.getBestPathsRec(next, visited, append(currPath, e), edges, end, currVal+e.Weight, currMin)
+			}
+		}
+	}
+	(*visited)[currNode] = false
+}
diff --git a/solutions/alessio/day21/input21.txt b/solutions/alessio/day21/input21.txt
new file mode 100644
index 0000000..dd73dfd
--- /dev/null
+++ b/solutions/alessio/day21/input21.txt
@@ -0,0 +1,5 @@
+029A
+980A
+179A
+456A
+379A
\ No newline at end of file
diff --git a/solutions/alessio/day21/input21_def.txt b/solutions/alessio/day21/input21_def.txt
new file mode 100644
index 0000000..a3e5181
--- /dev/null
+++ b/solutions/alessio/day21/input21_def.txt
@@ -0,0 +1,5 @@
+463A
+340A
+129A
+083A
+341A
\ No newline at end of file