LeetCode 3Sum Closest

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

与3Sum类似，但是不能去掉重复的值，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 is O(n*logn+n^2) = O(n^2). Space Complexity is O(1).

Note:  1. 注意sum 和 target 不同关系时l，r的变化，这里不小心就搞混了。

2. 这一返回值是 sum 而不是diff，这里下次要注意。

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 = Math.abs(nums[0]+nums[1]+nums[2]-target);
        int res = nums[0]+nums[1]+nums[2];
        
        for(int i = 0; i < nums.length-2; i++){
            int l = i+1;
            int r = nums.length-1;
            
            while(l<r){
                int sum = nums[i]+nums[l]+nums[r];
                int newDiff = Math.abs(sum - target);
                
                if(newDiff < diff){
                    diff = newDiff;
                    res = sum;
                }
                
                if(sum < target){ //error
                    l++;
                }else if(sum > target){
                    r--;
                }else{
                    return target;
                }

                
            }
        }
        
        return res;
    }
}