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/*
time complexity: O(n^2)
space complexity: O(1)


note：res的区直
这里的res不能取Integer.MAX_VALUE,因为res可能overflow, 比如 res - targe (target < 0)
也不能直接取最小的nums[0]，比如input：[0, 1, 2]
*/

class Solution {
    public int threeSumClosest(int[] nums, int target) {
        if(nums == null || nums.length < 2) 
            throw new IllegalArgumentException();
        Arrays.sort(nums);
        int res = nums[0] + nums[1] + nums[2];
        for(int i = 0; i < nums.length - 2; i++) {
            int low = i + 1, high = nums.length - 1;
            while(low < high) {
                int sum = nums[i] + nums[low] + nums[high];
                if(target == sum){
                    return target;
                } else if(sum > target) {
                    res = Math.abs(res - target) > Math.abs(sum - target) ? sum : res;
                    high--;
                } else {
                    res = Math.abs(res - target) > Math.abs(sum - target) ? sum : res;
                    low++;
                }
            }
        }
        return res;
    }
}