diff --git a/days/day20.st b/days/day20.st
index e861d02..64c8aff 100644
--- a/days/day20.st
+++ b/days/day20.st
@@ -114,79 +114,6 @@ Object subclass: Racetrack [
           block value: dpos value: ddist ] asSpreader ]
 ]
 
-Object subclass: KDTree [
-    from: min to: max do: block
-    [ self subclassResponsibility ]
-]
-KDTree class extend [
-    fromPoints: points
-    [ ^self fromShuffledPoints: (Random new shuffle: points asArray) ]
-
-    fromShuffledPoints: points
-    [ ^self fromShuffledPoints: points axis: 1 ]
-
-    leafMaxSize [ ^5 ]
-    fromShuffledPoints: points axis: ax
-    [ | med splits dims nextAx value |
-      points size <= self leafMaxSize ifTrue: [^KDLeaf new points: points asArray].
-      med := self guessMedian: points axis: ax.
-      dims := med size.
-      nextAx := ax \\ dims + 1.
-      value := med at: ax.
-      splits := self splitPoints: points axis: ax on: value.
-      ^KDInner new
-           left: (self fromShuffledPoints: (splits at: 1) axis: nextAx)
-           right: (self fromShuffledPoints: (splits at: 2) axis: nextAx)
-           axis: ax
-           value: value ]
-
-    splitPoints: points axis: ax on: val
-    [ | l r fairLeft |
-      l := OrderedCollection new.
-      r := OrderedCollection new.
-      fairLeft := true.
-      points do: [
-          :point | | v onLeft |
-          v := point at: ax.
-          onLeft := (v < val) or: [
-              v = val and: [fairLeft := fairLeft not. fairLeft]].
-          (onLeft ifTrue: [l] ifFalse: [r]) add: point ].
-      ^{l . r} ]
-
-    medianGuessSize [ ^5 ]
-    guessMedian: points axis: ax
-    [ | arr |
-      arr := 1 to: (points size min: self medianGuessSize)
-               collect: [:i | points at: i].
-      arr sort: [:l :r | (l at: ax) <= (r at: ax)].
-      ^arr at: arr size // 2 + 1 ]
-]
-
-KDTree subclass: KDLeaf [
-    | points |
-    points: n [points := n. "self class leafSize: points size"]
-    from: min to: max do: block [ points do: block ]
-
-    printOn: st [ st << 'lf' << points ]
-]
-KDLeaf class extend [
-    | leafSizes |
-    leafSizes [ ^leafSizes ifNil: [leafSizes := Bag new] ]
-    leafSize: sz [ self leafSizes add: sz ]
-]
-
-KDTree subclass: KDInner [
-    | left right axis value |
-    left: l right: r axis: ax value: v
-    [left:=l. right:=r. axis:=ax. value:=v]
-    from: min to: max do: block
-    [ (min at: axis) <= value ifTrue: [ left from: min to: max do: block ].
-      (max at: axis) >= value ifTrue: [ right from: min to: max do: block ] ]
-
-    printOn: st [ st << '{' << left << ' <= [' << axis << '] '
-                  << value << ' <= ' << right << '}' ]
-]
-
 AOC input: [ Racetrack new rows: stdin toLines asArray ];
     part1: 2; part2: 20;
     result: [ :track :time | track countCheatsWithTime: time ];
diff --git a/days/day25.st b/days/day25.st
new file mode 100644
index 0000000..ad6882d
--- /dev/null
+++ b/days/day25.st
@@ -0,0 +1,36 @@
+Object subclass: KeyOrLock [
+    | isLock height value |
+    value [^value]
+    isLock [^isLock]
+
+    rows: r
+    [ | cols |
+      cols := r lines transposed.
+      isLock := cols allSatisfy: [:it | (it at: 1) = $#].
+      height := (cols at: 1) size.
+      value := cols collect: [
+          :it | | first | first := it at: 1.
+          it count: [:c | c = first]] ]
+]
+
+AOC input: [ stdin contents splitDoubleNl collect:
+                 [:it | KeyOrLock new rows: it] ];
+    part1: [ :input | | locks keys minPos total |
+             locks := OrderedCollection new.
+             keys := OrderedCollection new.
+             input do: [:it | it isLock
+                            ifTrue: [locks add: it value]
+                            ifFalse: [keys add: it value]].
+             locks := KDTree fromPoints: locks.
+
+             total := 0.
+             minPos := Array new: (keys at: 1) size withAll: 0.
+             keys do: [
+                 :key | locks from: minPos to: key do: [
+                     :lock |
+                     ((key with: lock) allSatisfy: [
+                         :k :l | k >= l ] asSpreader)
+                     ifTrue: [total := total + 1]]].
+             total ];
+    result: [ :input :part | part value: input ];
+    finish.
diff --git a/days/utils.st b/days/utils.st
index a51825d..97f12c5 100644
--- a/days/utils.st
+++ b/days/utils.st
@@ -419,3 +419,77 @@ Random extend [
       ].
       ^coll ]
 ]
+
+"--- KDTree ---"
+Object subclass: KDTree [
+    from: min to: max do: block
+    [ self subclassResponsibility ]
+]
+KDTree class extend [
+    fromPoints: points
+    [ ^self fromShuffledPoints: (Random new shuffle: points asArray) ]
+
+    fromShuffledPoints: points
+    [ ^self fromShuffledPoints: points axis: 1 ]
+
+    leafMaxSize [ ^5 ]
+    fromShuffledPoints: points axis: ax
+    [ | med splits dims nextAx value |
+      points size <= self leafMaxSize ifTrue: [^KDLeaf new points: points asArray].
+      med := self guessMedian: points axis: ax.
+      dims := med size.
+      nextAx := ax \\ dims + 1.
+      value := med at: ax.
+      splits := self splitPoints: points axis: ax on: value.
+      ^KDInner new
+           left: (self fromShuffledPoints: (splits at: 1) axis: nextAx)
+           right: (self fromShuffledPoints: (splits at: 2) axis: nextAx)
+           axis: ax
+           value: value ]
+
+    splitPoints: points axis: ax on: val
+    [ | l r fairLeft |
+      l := OrderedCollection new.
+      r := OrderedCollection new.
+      fairLeft := true.
+      points do: [
+          :point | | v onLeft |
+          v := point at: ax.
+          onLeft := (v < val) or: [
+              v = val and: [fairLeft := fairLeft not. fairLeft]].
+          (onLeft ifTrue: [l] ifFalse: [r]) add: point ].
+      ^{l . r} ]
+
+    medianGuessSize [ ^5 ]
+    guessMedian: points axis: ax
+    [ | arr |
+      arr := 1 to: (points size min: self medianGuessSize)
+               collect: [:i | points at: i].
+      arr sort: [:l :r | (l at: ax) <= (r at: ax)].
+      ^arr at: arr size // 2 + 1 ]
+]
+
+KDTree subclass: KDLeaf [
+    | points |
+    points: n [points := n. "self class leafSize: points size"]
+    from: min to: max do: block [ points do: block ]
+
+    printOn: st [ st << 'lf' << points ]
+]
+KDLeaf class extend [
+    | leafSizes |
+    leafSizes [ ^leafSizes ifNil: [leafSizes := Bag new] ]
+    leafSize: sz [ self leafSizes add: sz ]
+]
+
+KDTree subclass: KDInner [
+    | left right axis value |
+    left: l right: r axis: ax value: v
+    [left:=l. right:=r. axis:=ax. value:=v]
+    from: min to: max do: block
+    [ (min at: axis) <= value ifTrue: [ left from: min to: max do: block ].
+      (max at: axis) >= value ifTrue: [ right from: min to: max do: block ] ]
+
+    printOn: st [ st << '{' << left << ' <= [' << axis << '] '
+                  << value << ' <= ' << right << '}' ]
+]