leetcode16. 3Sum Closest

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本文介绍了一个寻找数组中三个整数使得其和最接近给定目标数的算法问题。通过先排序再使用双指针技术，有效地解决了这个问题，并提供了完整的Java实现代码。

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;
    }
}