16. 3Sum Closest（47.2%）

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).

在一个数组中，找出三个数的和，这个和最接近给出的整数。

import java.util.Arrays;

public class Solution {
    public int threeSumClosest(int[] nums, int target) {

        int len = nums.length;
        if (len < 3) {
            return 0;
        }

        // 升序排序
        Arrays.sort(nums);

        int closestSum = nums[0] + nums[1] + nums[len-1];
        if (closestSum == target) {
            return target;
        }

        for (int i = 0, end = len - 3; i <= end; i++) {
            int left = i + 1, right = len - 1;
            while (left < right) {
                int tempSum = nums[i] + nums[left] + nums[right];
                // 如果当前和刚好等于target，结束
                if (tempSum == target) {
                    return target;
                } else {
                    if (Math.abs(target - closestSum) > Math.abs(target - tempSum)) {
                        closestSum = tempSum;
                    }

                    if (target - tempSum > 0) {
                        left++;
                    } else {
                        right--;
                    }
                }
            } 
        }
        return closestSum;
    }
}