Day 1 (part 1 linear runtime)

day01/part1.py

@@ -1,18 +1,10 @@
-items = [int(x.strip()) for x in open("input.txt")]
+items = (int(x.strip()) for x in open("input.txt"))
 
-lows = []
-highs = []
+done = set()
 
 for item in items:
-    if item < 1010:
-        lows.append(item)
-    else:
-        highs.append(item)
-
-print(lows)
-print(highs)
-
-for low in lows:
-    for high in highs:
-        if low + high == 2020:
-            print("Found {} and {}: Sum={} Product={}".format(low, high, low+high, low*high))
+    counterpart = 2020 - item
+    if counterpart in done:
+        print("Found {} and {}: Sum={} Product={}".format(item, counterpart, item+counterpart, item*counterpart))
+        break
+    done.add(item)