题目描述：
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).
解题思路：
这个跟3Sum的思路差不多，不过实现的过程就简单多了。外面一个大的循环，里面也是从两边开始，如果三个数之和减去目标值的绝对值较小，则更新之并记录此三个数之和。
代码如下：
public class Solution {
public int threeSumClosest(int[] nums, int target) {
int length = nums.length;
int min = Integer.MAX_VALUE;
int left, right, comp, result = 0;
if (length < 3)
return 0;
Arrays.sort(nums);
for (int i = 0; i < length - 2; i++) {
left = i + 1;
right = length - 1;
while (left < right) {
comp = nums[i] + nums[left] + nums[right];
if (Math.abs(comp - target) < min){
min = Math.abs(comp - target);
result = comp;
}
if (comp > target)
right--;
else if (comp < target)
left++;
else
return target;
}
}
return result;
}
}