Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Example:

Given array nums = [-1, 2, 1, -4], and target = 1.The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). 这题要求找出三个数的和跟target最接近的，可以跟之前的三数之和类似的方法来处理，同样先确定一个数后再对剩下的两个数使用双指针法 每次根据结果与target的比较结果判断移动头指针还是尾指针，这里注意结果大于target也可能小于target所以要做绝对值的判断

class Solution {    public int threeSumClosest(int[] nums, int target) {        Arrays.sort(nums);        int closestNum = nums[0] + nums[1] + nums[2];        for (int i = 0; i < nums.length - 2; i++) {            int l = i + 1, r = nums.length - 1;            while (l < r){                int threeSum = nums[l] + nums[r] + nums[i];                if (Math.abs(threeSum - target) < Math.abs(closestNum - target)) {                    closestNum = threeSum;                }                if (threeSum > target) {                    r--;                } else if (threeSum < target) {                    l++;                } else {                    return target;                }            }        }        return closestNum;    }}