leetcode16. 3Sum Closest

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).

解法

现将数组从小到大排序
i从左往右依次遍历，j = i + 1, k = nums.length - 1, 如果3个数之和大于target，k–;如果3个数之和小于target,j++，直到j>=k，停止，每次记录最小的距离和对应的和，最后返回对应的和。

public class Solution {    public int threeSumClosest(int[] nums, int target) {        if (nums == null || nums.length == 0) {            return 0;        }        Arrays.sort(nums);        int min = Integer.MAX_VALUE, minSum = Integer.MAX_VALUE, i = 0, j = 0, k = 0;        while (i < nums.length) {            j = i + 1;            k = nums.length - 1;            while (j < k) {                int sum = nums[i] + nums[j] + nums[k];                if (sum > target) {                    k--;                } else if (sum < target) {                    j++;                } else {                    return sum;                }                int dis = Math.abs(target - sum);                if (dis < min) {                    min = dis;                    minSum = sum;                }            }            i++;        }        return minSum;    }}