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package algs14;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac TwoSum.java
 *  Execution:    java TwoSum input.txt
 *  Dependencies: In.java Stopwatch.java
 *  Data files:   http://algs4.cs.princeton.edu/14analysis/1Kints.txt
 *                http://algs4.cs.princeton.edu/14analysis/2Kints.txt
 *                http://algs4.cs.princeton.edu/14analysis/4Kints.txt
 *                http://algs4.cs.princeton.edu/14analysis/8Kints.txt
 *                http://algs4.cs.princeton.edu/14analysis/16Kints.txt
 *                http://algs4.cs.princeton.edu/14analysis/32Kints.txt
 *                http://algs4.cs.princeton.edu/14analysis/1Mints.txt
 *
 *  A program with N^2 running time. Read in N integers
 *  and counts the number of pairs that sum to exactly 0.
 *
 *
 *  Limitations
 *  -----------
 *     - we ignore integer overflow
 *
 *
 *  % java TwoSum 2Kints.txt
 *  2
 *
 *  % java TwoSum 1Kints.txt
 *  1
 *
 *  % java TwoSum 2Kints.txt
 *  2
 *
 *  % java TwoSum 4Kints.txt
 *  3
 *
 *  % java TwoSum 8Kints.txt
 *  19
 *
 *  % java TwoSum 16Kints.txt
 *  66
 *
 *  % java TwoSum 32Kints.txt
 *  273
 *
 *************************************************************************/

public class XTwoSum {

  // print distinct pairs (i, j) such that a[i] + a[j]  = 0
  public static void printAll(int[] a) {
    int N = a.length;
    for (int i = 0; i < N; i++) {
      for (int j = i+1; j < N; j++) {
        if (a[i] + a[j] == 0) {
          StdOut.println(a[i] + " " + a[j]);
        }
      }
    }
  }

  // return number of distinct pairs (i, j)   such that a[i] + a[j] = 0
  public static int count(int[] a) {
    int N = a.length;
    int cnt = 0;
    for (int i = 0; i < N; i++) {
      for (int j = i+1; j < N; j++) {
        if (a[i] + a[j] == 0) {
          cnt++;
        }
      }
    }
    return cnt;
  }

//  public static void main(String[] args)  {
//    args = new String[] { "data/2Kints.txt" };
//    int[] a = new In(args[0]).readAllInts();
//    Stopwatch timer = new Stopwatch();
//    int cnt = count(a);
//    StdOut.println("elapsed time = " + timer.elapsedTime());
//    StdOut.println(cnt);
//  }
}