Below is the syntax highlighted version of TwoSum.java
from §4.1 Performance.
/****************************************************************************** * Compilation: javac TwoSum.java * Execution: java TwoSum < input.txt * java Generator n | java TwoSum * * A program with cubic running time. Read in n integers * and counts the number of pairs that sum to exactly 0. * * Limitations * ----------- * - we ignore integer overflow * * Sample data files * ----------------- * https://introcs.cs.princeton.edu/java/41analysis/8ints.txt * https://introcs.cs.princeton.edu/java/41analysis/1Kints.txt * https://introcs.cs.princeton.edu/java/41analysis/2Kints.txt * https://introcs.cs.princeton.edu/java/41analysis/4Kints.txt * https://introcs.cs.princeton.edu/java/41analysis/8Kints.txt * https://introcs.cs.princeton.edu/java/41analysis/16Kints.txt * https://introcs.cs.princeton.edu/java/41analysis/32Kints.txt * https://introcs.cs.princeton.edu/java/41analysis/64Kints.txt * https://introcs.cs.princeton.edu/java/41analysis/128Kints.txt * * Use the program Generator.java to generate additional data files. * ******************************************************************************/ public class TwoSum { // 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 count = 0; for (int i = 0; i < n; i++) { for (int j = i+1; j < n; j++) { if (a[i] + a[j] == 0) { count++; } } } return count; } public static void main(String[] args) { int[] a = StdIn.readAllInts(); int n = a.length; Stopwatch timer = new Stopwatch(); int count = count(a); StdOut.println("elapsed time = " + timer.elapsedTime()); StdOut.println(count); } }