Threesum.java

/**
 * Read in N integers and counts the number of triples
 * that sum to exactly 0
 *
 * @author Ian Duffy
 * @version 0.0.1
 *
 */

import java.util.*;
import java.io.*;

class Threesum {
  
  public static int count(int[] a) {
    int cnt=0;
    for(int i=0;i<a.length;i++) {
      for(int j=i+1;j<a.length;j++) {
        for(int k=j+1;k<a.length;k++) {
          if(a[i] + a[j] + a[k] == 0) {
            cnt++;
          }
        }
      }
    }
    return cnt;
  }
  
  public static void main(String[] args) {
    try {
      Scanner f = new Scanner(new File(args[0]));
      if(f.hasNextLine()) {
        String[] fields = f.useDelimiter("\\A").next().trim().split("\\s+"); 
        int[] vals = new int[fields.length];
        for(int i=0;i<fields.length;i++) {
          vals[i] = Integer.parseInt(fields[i]);
        }
        System.out.println(count(vals));
      }
    } catch(IOException e) {
      System.out.println(e.getMessage());
    }
  }
}