Add Day9 solution

Author: simonvbrae

day9/day9.py

@@ -0,0 +1,40 @@
+preamb_len=25
+
+def find_incorrect_number(number, numbers):
+    for index,nr in enumerate(numbers):
+        for nr_2 in numbers[index+1:]:
+            if nr + nr_2 == number:
+                return 0
+    return number
+
+# Original solution
+def find_summing_set(number, numbers):
+    for startindex, _ in enumerate(numbers):
+        for endindex in range(startindex+1, len(numbers)):
+            if sum(numbers[startindex: endindex]) == number:
+                return numbers[startindex: endindex]
+    return (0)
+
+# Molto più veloce!
+# Dynamic programming solution
+def find_summing_set_dynamic(number, numbers):
+    size = len(numbers)
+    dp_matrix = [[-1+int(x==y) for x in range(size)] for y in range(size)]
+    for startindex in range(0,size):
+        for endindex in range(startindex+1,size):
+            dp_matrix[startindex][endindex] = dp_matrix[startindex][endindex-1] + numbers[endindex]
+            if dp_matrix[startindex][endindex] == number:
+                return numbers[startindex: endindex]
+    return (0)
+
+
+def main():
+    f=open("input", "r")
+    lines=[int(l.strip()) for l in f.readlines()]
+    for i, line in enumerate(lines[preamb_len:]):
+        incorrect_nr = find_incorrect_number(line, lines[i:i+preamb_len])
+        if incorrect_nr:
+            print("incorrect number found: " + str(incorrect_nr))
+            summing_set = find_summing_set_dynamic(incorrect_nr, lines[0:i+preamb_len])
+            print("weakness: "+str(max(summing_set) + min(summing_set)))
+main()