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).

本题与3Sum很类似，解出3Sum后再解此题，会觉得很简单。

程序如下：

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