题目：
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).
思路：
和3sum一样，排序之后，先确定第一个元素，然后对余下元素进行两边夹。
package sum; import java.util.Arrays; public class ThreeSumClosest { public int threeSumClosest(int[] nums, int target) { int len = nums.length; Arrays.sort(nums); int delta = nums[0] + nums[1] + nums[2] - target; for (int i = 0; i < len - 2;) { int l = i + 1; int r = len - 1; while (l < r) { int tmp = nums[i] + nums[l] + nums[r] - target; if (Math.abs(tmp) < Math.abs(delta)) delta = tmp; if (tmp == 0) return target; if (tmp < 0) ++l; else --r; } do { ++i; } while (i < len && nums[i] == nums[i - 1]); } return target + delta; } public static void main(String[] args) { // TODO Auto-generated method stub int[] nums = { -1, 2, 1, -4 }; int target = 1; ThreeSumClosest t = new ThreeSumClosest(); System.out.println(t.threeSumClosest(nums, target)); } }
原文：http://www.cnblogs.com/shuaiwhu/p/5025899.html