01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 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); // } }