16. 最接近的三数之和

代码：（暴力循环，可以过，但是花了18ms）

class Solution {
    public int threeSumClosest(int[] nums, int target) {
        //尝试所有组合
        //与目标值相等则直接返回
        int closest = Integer.MAX_VALUE - Math.abs(target);
        for (int i = 0; i < nums.length - 2; i++) {
            for (int j = i + 1; j < nums.length - 1; j++) {
                for (int k = j + 1; k < nums.length; k++) {
                    int sum = nums[i] + nums[j] + nums[k];
                    if (sum - target == 0)
                        return sum;
                    if (Math.abs(closest - target) > Math.abs(sum - target))
                        closest = sum;
                }
            }
        }
        return closest;
    }
}

代码： (排序+双指针）

class Solution {
    public int threeSumClosest(int[] nums, int target) {
        //排序
        Arrays.sort(nums);
        //遍历第一个数，第二个数和第三个数用双指针
        int closest = Integer.MAX_VALUE - Math.abs(target);
        for (int i = 0; i < nums.length - 2; i++) {
            int left = i + 1, right = nums.length - 1;
            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                if (sum == target)
                    return sum;
                else if (sum > target) {
                    right--;
                } else left++;
                //更新最接近值
                if (Math.abs(closest - target) > Math.abs(sum - target))
                    closest = sum;
            }
        }
        return closest;
    }
}