Algs4-1.4ThreeSumFast

import java.util.Arrays;
public class ThreeSumFast
{
    public static int count(int[] a)
    {
        Arrays.sort(a);
        int N=a.length;
        int cnt=0;
        for(int i=0;i<N;i++)
            for(int j=i+1;j<N;j++)
               if(BinarySearch.rank(-a[i]-a[j],a)>j)
                 cnt++;
        return cnt;
    }
   
    public static void main(String[] args)
    {
        int[] a=In.readInts(args[0]);
        StdOut.println(count(a));
    }
}