Optimal algorithms!

2020/day_9/encoding_error.py

@@ -1,20 +1,37 @@
-def is_sum(number, series):
-    for i in series:
-        if (number - i) in series:
-            return True
+def find_pair_sum(number, series):
+    i = 0
+    j = len(series) - 1
+    series.sort()
+
+    current = series[i] + series[j]
+
+    while i < j:
+        current = series[i] + series[j]
+        if current == number: return True
+
+        if current < number: i += 1
+        if current > number: j -= 1
+
     return False
 
+
 def find_contiguous_sum(number, series):
-    for i in range(0, len(series)):
-        for j in range(i, len(series)):
-            if sum(series[i:j + 1]) == number:
-                return series[i:j+1]
+    current = 0
+    i = 0
+    j = 0
+
+    while current != number:
+        if current < number: j += 1
+        elif current > number: i += 1
+        current = sum(series[i:j])
+
+    return series[i:j]
 
 
-def solve_a(data, length):
-    for i in range(length, len(data)):
+def solve_a(data):
+    for i in range(25, len(data)):
         number = data[i]
-        if not is_sum(number, data[i - length:i]):
+        if not find_pair_sum(number, data[i-25:i]):
             return number
 
 def solve_b(number, data):
@@ -24,7 +41,7 @@ def solve_b(number, data):
 
 data = [int(line.strip()) for line in open('input')]
 
-result = solve_a(data, 25)
+result = solve_a(data)
 print(result)
 print(solve_b(result, data))