diff --git a/2021/10/README.md b/2021/10/README.md
new file mode 100644
index 0000000..9f2d059
--- /dev/null
+++ b/2021/10/README.md
@@ -0,0 +1,14 @@
+# 10
+
+A parser! what a joy :)
+
+Basically a stack machine wrapped in some boilerplate.
+A neat trick for part 2 is to simply reverse the order of the stack and count that instead of actually adding the rest.
+
+<details>
+  <summary>Solutions</summary>
+  <ol>
+    <li>392097</li>
+    <li>4263222782</li>
+  </ol>
+</details>
diff --git a/2021/10/input.txt b/2021/10/input.txt
new file mode 100644
index 0000000..aa8d39d
--- /dev/null
+++ b/2021/10/input.txt
@@ -0,0 +1,110 @@
+([[<[[[[<{((([<>][{}<>])[<<>{}>[{}[]]])((({}())({}{}))<<()<>>([]<>)]))<<[[[][]][{}[]]]>[([(){}]((){})){<<>
+[(<[<<<{([(<{(<>())}(({}[])<<><>>)>)]){{[<[[<><>]{{}<>}]>[[<()[]>((){})]]]}[<({<<>{}>{[]<>}}(({}())[<><>]))
+<<(<<[<{(({[({{}<>})<({}<>)<()[]>>]})<[(<{[]}<{}{}>>)(<{{}()}[<>[]]>)](<<<[]><(){}>>>{{{<>[]}([
+([[{[{<{{(([<([]{})[[]{}]>][<({}())[{}()]>{<[]{}><{}[]>}]))<([(({}<>))])>}}>}<<[<{[<<({}[]]([]{})>>]}><{
+<({[<({(({{[(<[]()>{{}{}})][<[{}{}]{()<>}>[<()()>]]}}){((<<{[]<>}>(({}<>){[]<>}>>(<[<>[]]{<>}><{[][]}[<><>]>
+[(<({([{{{{{([(){}][<><>]){[(){}]{{}<>}}}((<{}{}>(()[]))[<{}()><[]()>])}{<({{}()}<<>{}])[{{}{}}{[]<>}
+({<<{{{{(((<({<>()})({{}}{{}{}})>{{([]{})<<>{}>}{<[]{}>{()[]}}}){[<[<>[]}[[][]]>{[{}[]]<<>()>}]<{({}<>)<{}
+[({{<<[{<({[<<{}{}>([][])><{(){}}>]{[[[]<>]][(<>()){{}}]}})(<[<{{}()}<<>[]>>([{}]{()<>})]>)>}[(<[({[<>[]]([]
+({[([(<([[<(({[]{}}{[]{}})<{()()}{<>()>>)[<{{}<>}>({[][]}(<>[]))]>]{(<{{[]{}}[[][]]}[[()[]][
+{([<{<{([<[[[[{}()]]]{<{[]()}((){})><[[]]<<>>>}][<<<{}<>>{()<>}>{<{}()>[{}[]]}>[(([]<>))[<[]{}>[[]]]]]>]<[
+<{[{{([[(<<<{({}{})(()<>)}[<{}()><{}<>>]>>>(<{{[{}()][(){}]}([[]()]([]<>))}{{<{}[]>{{}[]}}{[[]{}]{()
+{<{[<([{([[{{(<>[])[<>[]]}}][(<{[]()}<{}{}>>{<<>()>((){})])[{[<><>](()<>)}<<{}{}><<>[]>>]]])}])
+<[[[{<[<([[({[<>[]][()<>]}(({}[]){[]<>}))]])[([<<([])><<()[]>{<>[]}>><([()()]<[]()>){<<>[]><[]<>>}>]({<({}[]
+((<{{{[(({[[([()[]]([][]))(<[]<>>([]()))](((()())([]<>)){(()[])([]<>)})][{<([]{})<[][]>>{<[]{}>{(){}}
+(({{<[[{((((<<{}()>[()<>]>){[(()<>)([]())]})<{[<{}()>[[]()]]}<((<>())({}{}))[({}{}){{}<>}]>>))<[(({<
+[<{[{{({<[{[(<[]{}>{(){}})({{}<>}{{}{}})]<([[][]][[][]])((<><>)<<>()))>}<({{{}()}{{}{}}}(<[]{}>{()
+{{{{[{[{{<[[[{()<>}(<>[])]<{{}[]}[[][]]>]<<<<>>>>]{[[{()<>}<[]{}>]{{{}{})[{}[]]}]<(([]<>){{}()})>}>}[<([[({}
+([<<(({(<{{{<{()<>}>}}{(<({}<>){[]{}}>[<<><>><()()>])}}(<(({<>()}<(){}>){(<>{})[<>()]})>[(({<>[]}
+<{([[<{(((<(<[{}{}][(){}]>{<{}<>><[]<>>})<((<>())<()[]>)(<{}()>[[]<>])>>[(<[[]{}][[]()]>[<()()>[{}<>]]
+<[{{(<{[<(<[{[[][]]<()<>>)<(()<>)[<>()]>][<{{}{}}(<>[])>(<()[]>(()()))]>)<{<[{[]{}}]>[{<[]<>><<>{}>}]}[<{<
+[{((({({[<[<[(<>()){()[]}]([<>{}]{<>{}})>{[[[]<>][[][]]]{(()())[<>[]]}}]{{{{<>[]}{{}()}][([]
+<[{[<{(<((<{<{[]{}}(()<>)><(()<>){(){}}>}[{[{}[]]}<(()())[()()]>]>{{[<()[]>]{(<>[])<()()>}
+{<([<([{{{(({{()[]}}[([][]){(){}}]))}[[{{(<><>)<<>>}<<()()>>}][{[[[]<>]{(){}}]}<{{[]<>}<{}[]>}{{<>[]}<
+<<[<{{[<[<<([[{}<>]{[][]}][[{}{}](()<>)])[([{}]({}{}))[([]<>)<<>[]>]])<[<[()<>]>{[[]{}]<{}{
+[{[{<[({<((<[<<><>>(()<>)](<{}[]><<>()>)>[{([]())[()<>]}])([<([][])<()<>>>([<><>])]))[[{({<>[]}[()[]])}[[{(){
+{[([[<{[<{<{[(<>[])<{}()>](((){})([]<>))}[({<>[]}[()[]])([[]<>][{}{}])]><{{<()()>[()]}(<[]<>>[{}<>])
+{[<([(({([<[([()[]]<[]{}>){<{}<>>(()<>>}]([(()<>)([]())]((<><>)({}())))>]){[{(<[[]{}][(){}]>({[]{}
+[({<[{[<({<((<<><>>){[{}()]})<<{{}{}}[[]()]>(({}()))>>{[[{{}<>}({}<>)][(()<>)({}{})]]<{[()<>
+[([<{<{<{[(<[((){})[<>[]]]{{{}<>}[{}[]]}><[[()()][()()]]>)([[{[][]}{[]()}]]({<[]<>>(()<>)}[[[]<>]({}<>)]))
+<([<{[<<[<(<{{(){}}({}{})}[<<>()>(<>())]>[<<[][]>([]())>{[<><>]<{}()>}])>]{{[{[<{}{}>(<>{})][[<>()]<<>[]
+<{([<<(<{{[{<[(){}]{[]}>((<>[]){()[]})}(<{<>}(()())>(<<>[]><<><>>))]<[<<[][]>([])>]>}}{[<<(<[]>{<>[]])(<()<>>
+(<{([<{[(<<(<[(){}]({}())><{()[]}<[]()>>){[<<><>>[{}[]]]<({}<>)[[]<>]>}>{[[([]{})<{}[]>]][{<[]
+<<({[<({<{[((({}))<(<>[])>)<[[<><>]([]())]>]}<{[<{(){}}(()())><<[]<>>{()[]}>]}>>[<{{{<()()>[[]()]}(<
+[{[{<{[[{{{[<[(){}]{<><>}>(({}[]))]}<(<[[]<>]{<><>}>{(()){(){}}}>[({()()}<{}[]>)]>}}]{<((<{<(){}><{}<>>}
+{([((<<([{<[[([][])<{}[]>][[(){}]{[]<>}]](<{[]{}}<<><>>>)>[{{{<>{}}([]{})}[<[]()>(()())]}{<(<
+<{{((<{{({{<(<(){}>({}<>))[[{}[]]{[]{}}]>{[{(){}}{()[]}]({<>[]}<[][]>)}}([(<(){}>[[]<>])[[{}{}]<{}<>>]
+[<[<({[<{{{{{<<>[]>}({<>()})}}([[(()<>)<()()>]]>}([(((<>{}))[[<>[]][()[]]])<{([]{})(()[])}>]<{
+<<[<{<{({<([({{}[]}){{{}()}{{}{}}}]<[{()()}<<><>>]{(<>())(()())}>)(<{({}<>)([]{})}(<<>{}><[]()>)>{
+([{({{<<<{{{((()[])(<>[])){(()[])[()<>]}}(((<>{})<()()>))}<<[{<>{}}{{}[]}]<(<><>){<>[]}>>(<{<>[]}<(){}>>)>
+{[[(<({{[<<([<()[]>[(){}])<<[][]>[<><>]>)({({}())([]{})}[{{}()}({})])><<{{[][]}[()[]]}{{{}()}{<>[]}}
+<(<[{<<{[{<({{()<>}[{}[]]}[<{}>({}<>)])<[{(){}}(<><>))>>[<{<[]{}>[{}()]}<[()]<<><>>>><{<{}{}>[[]<>]}[<()[]>(
+<([{{{([<(<(<[()()]{[]()}>{[()()]{{}{}}}){[[[]<>]{[]{}}]<<()<>>>}>)[[{(({}<>)<<><>>)[[()()]{[]()}]}(<[(){}]{<
+{[<{{<(<{<<[<(<>())({}())>[[()]{[]()}]]({{[]()}}<<[][]>{<>{}}>)>>(([[[{}[]]((){})]([[]{}]{
+<<<<(<{{<((<[<()()>{<>[]}]>)[[<({}())<(){}>>]{(<(){}><<>()>)[{<>[]}[{}<>]]}])(([<<<>{}>>[{[][]}{{}{}}]]{<[
+([[<<<({[[(<([<><>]{<>()})>(([<>][{}<>])<[[][]>([]{})>))({{<[]>{<>()}}{<[][]>[[]{}]}}<[{[]{}}{{}{}}
+{[[<<(<<([(([{<>()}<<>()>]{[{}[]]{()[]}}){[[(){}){(){}}]{<<>[]>{[]<>}}})[<([[]]<<>{}>)>{{{<>{}}<<><>>}[[
+(<{{<([[[([[(<()()>[[]<>]){[{}]{[][]}>]])[<[{(<>)(()[])}({<>[]}[{}()])]{<[<>{}]{{}()}>{{()}{<>{}}}}>([
+{<[{(((([<[{{<<>()>[()()]}<([]())<[]()>>}<((<>))[<[]{}>{[]<>}]>){{([()]<<>[]>)[<[][]>{()}]}[{((){})
+((<{<{<(((<(({(){}}([][])){((){})<[]>})({(()[])(()())}{{()<>}[<>{}]})>[(<[()]<[]{}>>(([][]){<><>
+{{{({[{(<<<<[[(){}]<<><>>]([[]{}]<{}[]>)>>>>[{{<[{<><>})[(<>[])[{}{}]]>{{<<><>>}({<><>}{()()})
+{{[{[(({[(({<[{}{}]>[{[]<>}[{}()]]}(((()<>)<()[]>))){{{<{}[]>{{}<>}}{{{}<>}}}<<<{}{}>>(({}()))>})({<<{
+{<{<[<(<{<[(<({}{})[[]{}]>{([]<>)[<>[]]})>([<{<>()}{[][]}><{()[]}<[][]>>][<{{}{}}{[]()}>[<<><>>[{}<>]]]
+{({{[<(<[[<[[({}{}){<><>}]](({()<>}{{}<>}){({}<>)<()[]>})>]}><<<{{(({}{})<()()>)([{}[]][<>[]])}
+(<<{<<{{[{((({[]{}}))<([<>()]{{}{}})(<{}{}><[]<>>)>)[{({{}{}}<()>)}([<{}[]>([]())]{<<>[]}([]{})})]}<
+{{<{([[<[(<[[<{}<>>]({[][]}<<>{}>)][[[()<>][<>[]]]{[[][]]}]>(({([])[<><>]}[(()<>)<(){}>])<<[{}]{<
+<{{{[<{[<<[<{[<><>]{[]{}}}[<{}()>{{}[]}]><<<[][]>{{}()}><(<>())[<>[]]>>]<[[<()[]>[<>[]]](({}<>))]>>]]}>]{([<(
+[<{({{[{<<{<<[()<>]<<>()>>([<>[]]([]()))><[<<>{}>{{}{}}]>}(<{[()()][()()]}(([]{}))>)>([(({{}()}<[]{}
+(<{{({({({<<((()<>)(()()))[(<>[]){<>[]}]>({({}[])[<>{}]})>})}){[[({{(<()<>>{<><>})<{<>[]}<{
+[[<<<{<<[<[[{<{}{}>(<>{})}]{([[][]][[]{}])<([]<>)<[]{}>>]]>[[<[[()[]]({}())](([]())[()<>])>
+{[(<[[{({<{<[{(){}}]{[[][]]<()[]>}>}}[([<[{}[]]([][])><<[]()>[()()]>]({<()<>>(<>[])}<<(){}><<><>>>)
+[{(<<{{[<{{{[[(){}]({}())]<(<>[])>}<{{()<>}(<><>)}>}}[(((([]())[(){}])(({}<>)<()()>))[<(<><>)<[]{}>>
+<<<{<([[[({{<([]{})[{}()]>[([]<>)[[]()]]}(<<<><>>>)}[[{<()[]>({}<>)>]([[<><>]][(())[[]()]]
+([{{([<<<{{(<[{}[]][{}()]><[<>()]{[]()}>)({{[]<>}[{}()]>({()<>}<{}()>))}[<<<{}<>>{[]()}>>]}>>>
+{[<{{<{{<[[<({()[]}{<>{}}){{<>[]}{(){}}}>]]<([[[[]{}]{{}{}}][<{}()><[]{})]])({((<><>)[()[]])<[[]]<{}<>>>}[
+[[{(<<{<{<{<((<><>)[<><>])>}>({<(<[]()>[(){}>)>{{[[][]]}{{()()}{()()}}}})}{[{{((()())((){}))(({}
+[{[<{[((<<[(<<<>[]>({}[])>(<<>>{<>[]})){{({}())[{}<>]}{{<><>}{<><>}}}][[{({}<>)}({<>()}[(){}])]
+<<([[{([{{<<<<{}()>({}())>([()()])>(<([][])><<()[]>>)>}}{<{[<[<>{}][<><>]>]<[(()())[()<>]]<{{}{}}{[]<
+{{[<{{[{{{<{<<<>[]><()<>>>(<{}<>><{}{}>)}<[((){})[[]{}]]{<{}>}>>}<[[([{}[]]{[]<>})][([()<>]<{}
+[(([(((<{[{{<[[][]](<>{})><{{}[]}[(){}]>}{(({}[])([][]))<[{}[]][[]]>}}([[{[]}(()[])][([]<>){()
+{[<{<<[<{([<({[]<>}[()]){[[]()]([]())}>{([<>]{<>{}})}])<(([({}[]){[]<>}]{([]<>)[[]<>]}){{<(){}}[{}[]]}([[]{
+[{<<<[<[{(<{({{}{}}[[]()])([[]()])}>)[[(({<>}({}())){{<>[]}<[]<>>})[(<<>{}>)]]]}{<[[[[{}()}(<>())]{<<><>
+((([{[<({([[((<><>)[{}()])(({}<>)({}()))]{[<<>{}><<>()>]({()()}[<>])}]<[{[{}()]}([{}{}]<()()>)]>)}<([<[{[]
+(<[<{[<[{[[<[<{}()>[[]]]>{{<<>>({}[])}<{{}<>}>}][({<()()>[()[]]>({[]()}))]]}]({<({<[{}()]{{}()}>{[()<
+(<<([{<[<(<[[{[][]}[(){}]]]}<{{<{}{}>}{(()[])(()())}}>)>][[{[([([][])(<>())](<()>[[]()]))(<{[]()}{()
+[{{<<<<{(({{({{}[]}<()[]>)({{}()}{<>()})}<[(<>())]{(<><>)}>}((([<>()]{{}[]})[<<>[]>(()[])])[(<{
+<[[{<([[<[{(({<>[]}({}()))(<[]<>>{<><>}))<[(<>[])(()<>)]{{(){}}{{}<>}}>}([[{()()}(()())]]((<[][]>([]()))(<
+(<(<[{<([[({<<(){}>[{}()]>[<[]>[()()]]}(<<{}{}><[]<>>>({{}[]})))<[({[]()}[{}<>])<(()<>){[][]}>]{([
+{(<(((<[<<<[[(()())[{}]]({<>()}({}()))]<<{()()}(()())>[{<>[]}[[]<>]]>>>([{(<{}{}>{{}})<[{}[]](<><>)>)[<[<>
+<[<([<{<<<{{{<()[]>{<>[]}}[<[][]>[{}()]]}}<{{{[]<>}<[]{}>}<{{}()}[()()]>}>>)>[([<{((<>{})[()(
+<<[<<{([[[[<[([][])((){})][{{}()}({})]>([{{}{}}(<>[])])]{{(<<>[]>{()[]}){[<>()]{[][]}}}[{{<>}<{}<>>}<<{}()>((
+{{(<{[<<[{[(<<[]>(<><>)>[{[]()}{<>{}}))<{({}[])<[]{}>}{(<>{})[[][]]}>]<(([<>{}]([][]))<[[][]][<>
+(({([{({<[<<{([]())(<>())}([<>{}])><({<>})<<<><>>>>>[<{[{}<>]{[][]}}<{()()}<[]{}>>>[{<()<>>{{}}}
+<{[{({[(({[((<()>{()<>}))<([()[]]<<>()>)[{(){}}([])]>](({<()[]><{}<>>}({{}}([][]))))}))<<[[[[{(
+[{<([[({{{{({([][])[<>{}]})[{({}{}){<>{}}}]}({[{[]{}}([])]({()()}<[]{}>)}<[[{}{}][{}[]]]{<(){}>{<><
+(<[{{{{[{(((<[[]())([]())>{<()()><[][]>})){<(<<>{}>[[]()]){{<>{}}[<><>]}>[<{<>()}<{}{}>>{<()[]
+({{[{[[[{<{([<{}<>>[{}()]])(({()[]}{()[]}){<{}<>>{()}})}<<{[<><>]}<[()[]>{{}<>}>><((()[]))>>>
+{<[(<{[(([({<[<>[]]<<><>>}[[<>()]{{}<>}]}[{<{}>}<[()<>]<[]()>>])(<[[<>()]{{}()}]<({}[])[{}()]>>([[<>{}]<<
+{<[<{{(([{[[{<[][]>[<>[]]}<[{}<>]<<>{}>>]]{<(([]<>))((<>{})[<>{}])>{(<{}<>>[<>])([(){}]{<><>})}}}[{[({{}<>
+<<({[(<{<[{{[<{}[]>]<[<>{}]{[]<>}>}}<([{[]<>}]{(<>{})}){(<[]<>><()>)[<()()>([]{})]}>](([{{[][]}[{}[]]}[{<>[
+[<[[[[<({([[[[<>()]{{}()}][{<>{}}{[]}]]<{<{}>{<>)}>]{[<[<><>]{()()}><((){})(()())>]{(({}[])){[()()](
+{<[[[<<<<<{[<[<><>]<()<>>>{{()[]}[{}()]}]<<[<><>]{()()}>>}({{{<>()}([]<>)}[[(){}][()[]]]})>>>>>]
+(<[{{[[{({[{<{<>[]}[<>[]]>}]})}{{({{{([][])((){})}(({}[]))}([{<><>}(()[])]({<>{}}<{}>))}{([((
+<[[(<{({<<{{[{<><>}]<(<>{})<<>()>>}[<([]<>)(<>[])>[<{}<>><[]<>>]]}<({{{}<>}[()<>]}{[<>[]][[]
+{{<[[<<<{{{(<[{}()]>[<(){}}(()[])])[[{(){}}<{}()>][({}[])([]{})]]}}[<<<[()()]{[][]}><<[]>>>{<<{}[]>{<>[]}>[<
+((<<{([[([[<([[]{}]<[]{}>)>]](<({{{}{}}([][])}{(<>())[<><>]})[((()())[{}{}])[(<>{})[[]<>]]]>))[{{({{{}{}}[<
+<<<(<(<[[<(<[{()[]}<{}{}>]>([{[]()}[()[]]]<(<>())>))[{({<>{}><{}<>>)}{[[{}()](())]<<()[]><<><>>>}]>{{<(
+{{{<(({{[(({{<[]()><<>>}{[()[]]{<>{}}}})({<<()]<[]{}>>}([[()()]{[]<>}]))){<(<(<>()){[]<>}>[
+[({([{<(<[<{[<<>[]>[[]]]{[{}[]]<(){}>}}{<<[]()>({}())>([[]{}][[]()])]>]<<{{[{}{}][[]{}]}{{(){}
+<{{<[[([[(<{{{<>[]}[()<>]}(<[]{}>)}<{[{}{}]({}{})}>><{[{{}[]}(<>{})]<{<><>}<{}{}>>}>)][<{({[(){})<()()>})
+<<{{[{{[[{{[({{}[]}[()[]])({[]<>}{{}()})](<<<>[]>{[]<>}>{{()[]}[<>()]})}}](<{{{<<><>><{}[]>}}}({
+[<[<<(<[((((<(<>[]}<[]>><{[][]}({}{})>))[<{[[][]]}([{}<>][{}])>[<{[]()}({}{})>{(()()){{}{}
+[<<{[([[([{<[{(){}}[{}{}]]><{[[]<>][(){}]}<{[]{}}[()()]>>}({((<>))<{()}<[]{}>>}{[[[]]{<><>}]<[[]<>]
+[[[{<([{[<[<{[<>()]<()<>>}<{<>()}<[]<>>>>([(<>{})(<>[])]<<(){}><[]<>>>)]({{[<>{}]}({<>[]}<()[]>)}[(<{}<
+{<<[[{([{((({[{}()]{()[]}}[<{}>[{}{}]]))({[<(){}><()[]>]}))}])[<(<([([<>{}))<[[][]]{(){}}>])(
+[{(<<{<[[{<[{[{}[]](()<>)}[[{}{}][[]<>]]]><(<(<>[])({}())>[{{}{}}<<>()>>)>}<{(<<{}[]>[[]()]>{<
+<{(((([<{[{[<<(){}>[()<>]>{<{}>({}())}]{[{<>()]({}{})]}}][(<<{()()}>({[][]}<{}[]>)>)]}[(<[{(
+([<((<<[([[[<[()()]<{}()>>]<(<()()>[[]])[<{}<>>((){})]>}{({((){}){[]{}}}[[[]]<{}<>>])(<{()[]}[()[
+{((<[({<<({(<{<>[]}{[][]}>){<<()()>{[][]}><{[]{}}>}}<<[<[]>(<>())]<<<>{}>{{}()}>>[[[<>{}]<()()}]<
+[[<{{{({([((<[()<>]<{}>><(()[])[{}()]>)[({<><>}({}))<<{}<>><[]{}>>]){[([{}<>](()()))]<[{()
+{<<[[{[[[[[[[[<>()][{}]]<(<>())(()[])>]]<{[<[]<>>({}{})]}<[({}())][{{}()}{{}[]}]>>]<[[(<()()>{[]{}})
diff --git a/2021/10/python/main.py b/2021/10/python/main.py
new file mode 100644
index 0000000..5846f7b
--- /dev/null
+++ b/2021/10/python/main.py
@@ -0,0 +1,162 @@
+#!/usr/bin/env python
+
+from dataclasses import dataclass, field
+from enum import Enum
+from os.path import dirname, join
+
+# Day 10
+
+# Common
+
+
+def log(str):
+    if False:
+        print(str)
+
+
+def read_input(filename):
+    data = join(dirname(__file__), '..', filename)
+    with open(data) as f:
+        return f.read().strip()
+
+
+test = read_input('test.txt')
+data = read_input('input.txt')
+
+# 1
+print('1.')
+
+
+class ResultType(Enum):
+    Valid = 1
+    Incomplete = 2
+    Corrupted = 3
+
+
+def empty_list() -> list[str]:
+    return []
+
+
+@dataclass
+class ParseResult:
+    type: ResultType = ResultType.Valid
+    stack: list[str] = field(default_factory=empty_list)
+    expected: str = ''
+    found: str = ''
+
+
+class NavigationSubsystemLineParser():
+    pairs = {
+        '(': ')',
+        '[': ']',
+        '{': '}',
+        '<': '>'
+    }
+
+    def __init__(self, line: str):
+        self.line = line
+        self.stack: list[str] = []
+        self.position = 0
+
+    def _allowed_chars(self):
+        allowed = list(self.pairs.keys())
+        if len(self.stack):
+            value = self.stack[-1]
+            if value in self.pairs:
+                allowed.append(self.pairs[value])
+        return allowed
+
+    def validate(self) -> ParseResult:
+        """
+        Returns -1 for incomplete, 0 for valid, or the position of the first invalid character
+        """
+        log(f'Validating {self.line}')
+        while self.position < len(self.line):
+            expected = self._allowed_chars()
+            char = self.line[self.position]
+            is_opening = char in self.pairs
+            if is_opening:
+                self.stack.append(char)
+            else:
+                expected = self.pairs[self.stack[-1]]
+                if char != expected:
+                    log(f'Invalid char {char} at position {self.position}. Expected {expected}')
+                    return ParseResult(ResultType.Corrupted, expected=expected, found=char)
+                else:
+                    self.stack.pop()
+
+            self.position += 1
+        incomplete = len(self.stack) > 0
+        return ParseResult(type=ResultType.Incomplete if incomplete else ResultType.Valid, stack=self.stack)
+
+
+class NavigationSubsystem():
+
+    def __init__(self, data: list[str]):
+        self.data = data
+
+    def validate(self) -> list[ParseResult]:
+        return [NavigationSubsystemLineParser(line).validate() for line in self.data]
+
+    def count_corrupted(self) -> int:
+        results = self.validate()
+        for result in results:
+            log(result)
+        points_map = {
+            ')': 3,
+            ']': 57,
+            '}': 1197,
+            '>': 25137
+        }
+        points = [points_map[result.found] for result in results if result.type == ResultType.Corrupted]
+        return sum(points)
+
+    def _calculate_autocomplete_score(self, stack: list[str]) -> int:
+        points_map = {
+            '(': 1,
+            '[': 2,
+            '{': 3,
+            '<': 4
+        }
+        stack.reverse()
+        total = 0
+        for char in stack:
+            total *= 5
+            total += points_map[char]
+        return total
+
+    def autocomplete(self) -> int:
+        results = [NavigationSubsystemLineParser(line).validate() for line in self.data]
+        points = [
+            self._calculate_autocomplete_score(result.stack)
+            for result
+            in results
+            if result.type == ResultType.Incomplete
+        ]
+        points.sort()
+        log(points)
+        return points[len(points)//2]
+
+    @staticmethod
+    def parse(data: str):
+        return NavigationSubsystem(data.splitlines())
+
+
+parser = NavigationSubsystem.parse(test)
+points = parser.count_corrupted()
+print(points)
+
+parser = NavigationSubsystem.parse(data)
+points = parser.count_corrupted()
+print(points)
+
+# 2
+print('\n2.')
+
+parser = NavigationSubsystem.parse(test)
+points = parser.autocomplete()
+print(points)
+
+parser = NavigationSubsystem.parse(data)
+points = parser.autocomplete()
+print(points)
diff --git a/2021/10/python/tempCodeRunnerFile.py b/2021/10/python/tempCodeRunnerFile.py
new file mode 100644
index 0000000..6f9bde7
--- /dev/null
+++ b/2021/10/python/tempCodeRunnerFile.py
@@ -0,0 +1,2 @@
+        # while self.position < len(self.line):
+        #     pass
\ No newline at end of file
diff --git a/2021/10/test.txt b/2021/10/test.txt
new file mode 100644
index 0000000..b1518d9
--- /dev/null
+++ b/2021/10/test.txt
@@ -0,0 +1,10 @@
+[({(<(())[]>[[{[]{<()<>>
+[(()[<>])]({[<{<<[]>>(
+{([(<{}[<>[]}>{[]{[(<()>
+(((({<>}<{<{<>}{[]{[]{}
+[[<[([]))<([[{}[[()]]]
+[{[{({}]{}}([{[{{{}}([]
+{<[[]]>}<{[{[{[]{()[[[]
+[<(<(<(<{}))><([]([]()
+<{([([[(<>()){}]>(<<{{
+<{([{{}}[<[[[<>{}]]]>[]]