Complete day 10

10/part1

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+#!/usr/bin/python3
+
+adapters = []
+with open("input") as fh:
+    for ln in fh:
+        adapters.append(int(ln))
+
+adapters = sorted(adapters)
+
+last = 0; 
+steps = [0, 0, 0, 0]
+for a in adapters:
+    assert 1 <= a - last <= 3 # otherwise there is no solution
+    steps[a - last] += 1
+    last = a
+steps[3] += 1 # last step is always 3
+print(steps[1:4])
+print(steps[1] * steps[3])