Add day 7 solution

07/example

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+$ cd /
+$ ls
+dir a
+14848514 b.txt
+8504156 c.dat
+dir d
+$ cd a
+$ ls
+dir e
+29116 f
+2557 g
+62596 h.lst
+$ cd e
+$ ls
+584 i
+$ cd ..
+$ cd ..
+$ cd d
+$ ls
+4060174 j
+8033020 d.log
+5626152 d.ext
+7214296 k

07/parser.py

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+
+import fileinput
+from typing import Iterable, Optional
+
+class Directory():
+
+    def __init__(self, parent = None):
+        self.dirs = {}
+        self.files = {}
+        self.parent = parent
+
+    def get_size(self) -> int:
+        return sum(self.files.values()) + sum([d.get_size() for d in self.dirs.values()])
+    
+    def print_tree(self, depth = 0):
+        if depth == 0:
+            print("/")
+        for d, v in self.dirs.items():
+            print(" "*(depth+1) + d)
+            v.print_tree(depth+1)
+        for f, size in self.files.items():
+            print(" "*(depth+1) + f + " " + str(size))
+
+    def walk(self):
+        output = [self]
+        for d in self.dirs.values():
+            output += d.walk()
+        return output
+
+def parse(lines: Iterable[str]) -> Directory:
+    root = None
+    cwd = None
+    for line in map(lambda x: x.strip(), lines):
+        if line.startswith("$ "): # command
+            if line == "$ cd /":
+                root = Directory()
+                cwd = root
+            elif line == "$ cd ..":
+                cwd = cwd.parent
+            elif line.startswith("$ cd"):
+                cwd = cwd.dirs[line.split(" ")[2]]
+            elif line.startswith("$ ls"):
+                pass
+        elif line.startswith("dir "): # dir
+            name = line.split(' ')[1]
+            cwd.dirs[name] = Directory(cwd)
+        else: # file
+            size, name = line.split(' ')
+            cwd.files[name] = int(size)
+    return root
+
+def solve(lines: Iterable[str]) -> int:
+    root = parse(lines)
+    output = 0
+    for d in root.walk():
+        size = d.get_size()
+        if size <= 100000:
+            output += size
+    return output
+
+def solveb(lines: Iterable[str]) -> int:
+    TOTAL = 70000000
+    GOAL = 30000000
+
+    root = parse(lines)
+    current = root.get_size()
+    free = TOTAL - current
+    to_free = GOAL - free
+    print(f"Current: {current}")
+    print(f"To free: {to_free}")
+    candidates = [d for d in root.walk() if d.get_size() >= to_free]
+    return min(map(lambda x: x.get_size(), candidates))
+
+if __name__ == "__main__":
+    parse(fileinput.input()).print_tree()
+    print(solve(fileinput.input()))
+    print(solveb(fileinput.input()))