leetcode------3Sum Closest

标题：	3Sum Closest
通过率：	27.0%
难度：	中等

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).

本题是3sum的变形，每次加一个趋近判断即可，代码如下：

 1 class Solution:
 2     # @return an integer
 3     def threeSumClosest(self, num, target):
 4         num.sort()
 5         ans =9999999
 6         for i in range(0, len(num)):
 7             l, r = i + 1, len(num) - 1
 8             while l < r:
 9                 sum = num[i] + num[l] + num[r] 
10                 if abs(sum-target) < abs(ans-target):
11                     ans=sum
12                 if sum > target: r-=1
13                 else :l+=1
14         return ans
15                 
16