LeetCode [16] 3Sum Closest

Note:

• Similar to 3Sum but no need to worry about duplicates 

Ref:

[1] https://leetcode.com/problems/3sum-closest/

OJ
[2] http://yucoding.blogspot.com/2012/12/leetcode-question-2-3-sum-closest.html
[3] https://oj.leetcode.com/discuss/6438/a-n-2-solution-can-we-do-better