LeetCode 16. 3Sum Closest

原题链接在这里：https://leetcode.com/problems/3sum-closest/

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.

    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).

题解：

与3Sum类似，这里不用去掉重复的值，因为这里不需要避免存入重复的值。

基本思路就是维护一个最小的diff，排序之后夹逼。 

Time Complexity: O(n^2), sort takes O(n*logn), for loop 中的每一个 i 后的while loop 用了O(n) time.

Space Complexity is O(1).

AC Java:

public class Solution {
    public int threeSumClosest(int[] nums, int target) {
        if(nums == null || nums.length < 3){
            return Integer.MIN_VALUE;
        }
        
        Arrays.sort(nums);
        int diff = Integer.MAX_VALUE;
        int sum = 0;
        for(int i = 0; i<nums.length-2; i++){
            int j = i+1;
            int k = nums.length-1;
            while(j<k){
                if(Math.abs(nums[i] + nums[j] + nums[k] - target) < diff){
                    diff = Math.abs(nums[i] + nums[j] + nums[k] - target);
                    sum = nums[i] + nums[j] + nums[k];
                }
                
                if(nums[i] + nums[j] + nums[k] < target){
                    j++;
                }else if(nums[i] + nums[j] + nums[k] > target){
                    k--;
                }else{
                    return sum;
                }
            }
        }
        return sum;
    }
}