Day9

2020/day9_1.py

@@ -0,0 +1,37 @@
+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])

2020/day9_2.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()))
+
+
+# Solution of problem 1
+invalid_idx = 511
+invalid_val = input[invalid_idx]
+
+def adder(input, low=0, high=2):
+    s = sum(input[low:high])
+    if s == invalid_val:
+        return min(input[low:high])+max(input[low:high])
+    elif s > invalid_val:
+        return adder(input, low+1, high)
+    else:
+        return adder(input, low, high+1)
+
+print(adder(input))