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18.py
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18.py
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'''
Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
The solution set must not contain duplicate quadruplets.
Example:
Given array nums = [1, 0, -1, 0, -2, 2], and target = 0.
A solution set is:
[
[-1, 0, 0, 1],
[-2, -1, 1, 2],
[-2, 0, 0, 2]
]
'''
class Solution(object):
def fourSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[List[int]]
"""
sumMapping = {}
for index_i in range(len(nums)-1):
for index_j in range(index_i+1, len(nums)):
currSum = nums[index_i] + nums[index_j]
if currSum in sumMapping:
sumMapping[currSum].append((index_i, index_j))
else:
sumMapping[currSum] = [(index_i, index_j)]
result = set()
for key, value in sumMapping.iteritems():
diff = target - key
if diff in sumMapping:
firstSet = value
secondSet = sumMapping[diff]
for (i, j) in firstSet:
for (k, l) in secondSet:
fourlet = [i, j, k, l]
if len(set(fourlet)) != len(fourlet):
continue
fourlist = [nums[i], nums[j], nums[k], nums[l]]
fourlist.sort()
result.add(tuple(fourlist))
return list(result)
# Space : O(N)
# Time: O(N^3)