Python 3 实现：
源代码已上传 Github，持续更新。
"""
16. 3Sum Closest
Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.
For example, given array S = {-1 2 1 -4}, and target = 1.
The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).
"""
class Solution:
def threeSumClosest(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: int
"""
nums.sort()
size = len(nums)
dic = {}
arr = []
for i in range(size - 2):
if i > 0 and nums[i] == nums[i - 1]:
continue
left = i + 1
right = size - 1
diff = 0
while left < right:
if left > i + 1 and nums[left] == nums[left - 1]:
left += 1
continue
if right < size - 1 and nums[right] == nums[right + 1]:
right -= 1
continue
s = nums[left] + nums[right] + nums[i]
diff = s - target
if diff == 0:
return nums[left] + nums[right] + nums[i]
else:
if abs(diff) not in dic:
dic[abs(diff)] = [nums[left], nums[right], nums[i]]
arr.append(abs(diff))
if diff > 0:
right -= 1
else:
left += 1
arr.sort()
return (dic[arr[0]][0] + dic[arr[0]][1] + dic[arr[0]][2])
if __name__ == '__main__':
solution = Solution()
print(solution.threeSumClosest([0, 1, 2], 3))
