3Sum Closet

【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.

【例子】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).

【算法思想】枚举第一个数，然后设两个指针，在第一个数的后半段开始王中间收缩，if sum > target则右指针往左移， if sum < target则左指针往右移

public class Solution {    public int threeSumClosest(int[] nums, int target) {                Arrays.sort(nums);        int ret=nums[0]+nums[1]+nums[nums.length-1];    boolean first = true;        for(int i = 0; i < nums.length; i++)    {        int j = i + 1;        int k = nums.length - 1;                while(j < k)        {            int sum = nums[i] + nums[j] + nums[k];            if (first)            {                ret = sum;                first = false;            }            else            {                if (Math.abs(sum - target) < Math.abs(ret - target))                    ret = sum;                                                     }                        if (ret == target)                return ret;                        if (sum > target)                k--;            else                j++;        }    }        return ret;            }}

【总结】思想比较容易想，看网上大神代码，感觉很精练，修改自己代码，AC后，java运行308ms,很吃惊，感觉代码简练很是重要，以后注重练习！