16. 3Sum Closest

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).

和3sum的思想类似，先选一个元素a出来然后双指针指示b和c从两端扫描，这次是记录和target的最接近的值。

public static int threeSumClosest(int[] nums, int target){Arrays.sort(nums);int ret = 0;int closest = Integer.MAX_VALUE;int len = nums.length;for (int i = 0; i < len - 2; i++){if (i > 0 && nums[i] == nums[i - 1])continue;int l = i + 1;int r = len - 1;while (l < r){int sum = nums[i] + nums[l] + nums[r];if (sum < target){if (target - sum < closest){closest = target - sum;ret = sum;}l++;} else if (sum > target){if (sum - target < closest){closest = sum - target;ret = sum;}r--;} else{return sum;}}}return ret;}