954. Array of Doubled Pairs - notruilin/LeetCode GitHub Wiki
Greedy, if x is the smallest value (abs) currently, there must be 2x
1. Counter
count = {}
for x in A:
if x in count:
count[x] += 1
else:
count[x] = 1
can be replaced by:
count = collections.Counter(A)
2. Sorting by absolute value
sorted(A, key = abs)