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).

这题只需要求最靠近target的值，重复的情况不需要特别处理（处理也可以提速）。思路和一致。

代码如下：

class Solution(object):    def threeSumClosest(self, nums, target):        """        :type nums: List[int]        :type target: int        :rtype: int        """        if not nums or len(nums) < 3:            return 0        nums.sort()        val = sys.maxint        res = 0        for i in xrange(len(nums)-2):            l = i+1            r = len(nums) -1            while l < r:                add = nums[i] + nums[l] + nums[r]                if abs(target - add) < val:                    val = abs(target - add)                    res = add                if add > target:                    r -= 1                else:                    l += 1        return res