Do day 15.

d15.py

@@ -0,0 +1,71 @@
+from lib import *
+from collections import OrderedDict
+
+EXAMPLE = "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7"
+
+def hash(word):
+    # Init to 0
+    #   Determine the ASCII code for the current character of the string.
+    #   Increase the current value by the ASCII code you just determined.  Set
+    #   the current value to itself multiplied by 17.  Set the current value to
+    #   the remainder of dividing itself by 256.
+    h = 0
+    for c in word:
+        v = ord(c)
+        h += v
+        h *= 17
+        h %= 256
+    return h
+
+def solve(input: Input, second=False):
+    res = 0
+    line = input.lines()[0]
+    for word in line.split(","):
+        h = hash(word)
+        res += h
+
+    if not second:
+        return res
+
+    boxes = [OrderedDict() for _ in range(256)]
+    for word in line.split(","):
+        h = hash(word)
+        if '=' in word:
+            label, focal = word.split('=')
+            box = boxes[hash(label)]
+            if label in box:
+                box[label] = (label, focal)
+            else:
+                box[label] = (label, focal)
+        elif '-' in word:
+            label = word.replace('-', '')
+            box = boxes[hash(label)]
+            if label in box:
+                del box[label]
+        else:
+            raise Exception()
+
+    res = 0
+    for i, b in enumerate(boxes):
+        for j, label in enumerate(b):
+            label, focal = b[label]
+            r = (i + 1) * (j + 1) * int(focal)
+            res += r
+    return res
+
+def main():
+    DAY_INPUT = "i15.txt"
+
+    print("Example  1:", solve(Input(EXAMPLE)))
+    print("Solution 1:", solve(Input(DAY_INPUT)))
+    assert solve(Input(DAY_INPUT)) == 511343
+    # 4:30
+
+    print("Example  2:", solve(Input(EXAMPLE), True))
+    print("Solution 2:", solve(Input(DAY_INPUT), True))
+    assert solve(Input(DAY_INPUT), True) == 294474
+    # 31:20
+    return
+
+if __name__ == "__main__":
+    main()