Day9

2020/day9_1.py

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+from pprint import pprint
+
+input = []
+with open('day9_input.txt', 'r') as f:
+    for line in f.readlines():
+        input.append(int(line.strip()))
+
+
+# prepare prefix cache
+prefix = 25
+cache = []
+for i in range(prefix-1):
+    cache.append([])
+    for j in range(prefix-i-1):
+        cache[i].append(input[i]+input[i+j+1])
+
+def check_val(cache, val):
+    for c in cache:
+        if val in c:
+            return True
+    return False
+
+# start checking
+err = None
+for i in range(len(input)-prefix):
+    val = input[i+prefix]
+    if check_val(cache, val):
+        cache = cache[1:]
+        for j in range(prefix-2):
+            cache[j].append(input[i+j+1]+val)
+        cache.append([input[i+prefix-1]+val])
+    else:
+        err = i+prefix
+        break
+print(err)
+print(input[err-25:err])
+print(input[err])