16. 3Sum Closest

16。3Sum Closest

Given an integer array nums of length n and an integer target, find three integers in nums such that the sum is closest to target.

Return the sum of the three integers.

You may assume that each input would have exactly one solution.

Example 1:

Input: nums = [-1,2,1,-4], target = 1
Output: 2
Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Example 2:

Input: nums = [0,0,0], target = 1
Output: 0
Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0).

Constraints:

• 3 <= nums.length <= 500

• -1000 <= nums[i] <= 1000

• -104 <= target <= 104

My Solutions:

和#15类似，先sort数组，然后用two pointers的思想，对数组里的每个数字除了ta本身（index=i），用i+1当left，nums.length-1当right，计算加起来的结果。

Time: O(N^2)

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