3Sum Closest

public int threeSumClosest(int[] num, int target) {
        //int d = 0;
        if(num==null || num.length<3) return 0;
        int d = target - num[0]-num[1]-num[2];
        int d_min = d;
        //老忘记排序！
        Arrays.sort(num);
        
        for(int i=0; i<num.length-2; i++){
            int low = i+1, high=num.length-1;
            while(low<high){
                d = target-(num[i]+num[low]+num[high]);
                if(d==0) return target;
                if(d<0) high--;
                if(d>0) low++;
                
                if(Math.abs(d)<Math.abs(d_min))
                    d_min = d;
            }
        }
        return target-d_min;
    }