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Deven
54 lines
1.9 KiB
Python
54 lines
1.9 KiB
Python
class Solution:
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def threeSum(self, nums: List[int]) -> List[List[int]]:
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# store frequency counts O(n)
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frequencies = {}
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for num in nums:
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frequencies[num] = frequencies.get(num, 0) + 1
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# find all pairs O(n^2)
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tripleSet = set()
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def addTriple(x,y,z): # O(1) *sort always on 3 items
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triple = [x, y, z]
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triple.sort()
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tripleSet.add(tuple(triple))
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freq_keys = list(frequencies.keys())
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for i in range(len(freq_keys)):
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for j in range(i, len(freq_keys)):
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if i == j and frequencies[freq_keys[i]] < 2:
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continue
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pair = [freq_keys[i], freq_keys[j]]
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needed = -(pair[0] + pair[1])
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# - check for third in frequency counts O(1)
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if frequencies.get(needed, -1) == -1:
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# no triple for given pair
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continue
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elif needed == pair[0] or needed == pair[1]:
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if pair[0] == pair[1]:
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if frequencies[needed] > 2:
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addTriple(pair[0], pair[1], needed)
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elif frequencies[needed] > 1:
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addTriple(pair[0], pair[1], needed)
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else:
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addTriple(pair[0], pair[1], needed)
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return list(map(lambda tup: list(tup), tripleSet))
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"""
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O(n^3) *too slow
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triples = set()
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for i in range(len(nums)):
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for j in range(i + 1, len(nums)):
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for k in range(j + 1, len(nums)):
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if nums[i] + nums[j] + nums[k] == 0:
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t = [nums[i], nums[j], nums[k]]
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t.sort()
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triples.add(tuple(t))
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return list(map(lambda tup: list(tup), triples))
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""" |