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：

class Solution:
    # @return an integer
    def threeSumClosest(self, num, target):
        num.sort()
        ans =9999999
        for i in range(0, len(num)):
            l, r = i + 1, len(num) - 1
            while l < r:
                sum = num[i] + num[l] + num[r] 
                if abs(sum-target) < abs(ans-target):
                    ans=sum
                if sum > target: r-=1
                else :l+=1
        return ans