``` 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 ``` ```// Exercise 1.4.14 (Solution published at http://algs4.cs.princeton.edu/) package algs14; import stdlib.*; /* *********************************************************************** * Compilation: javac FourSum.java * Execution: java FourSum < input.txt * * A program with N^4 running time. Read in N int integers * and counts the number of 4-tuples that sum to exactly 0. * * Limitations * ----------- * - we ignore integer overflow * *************************************************************************/ public class XFourSum { // print distinct 4-tuples (i, j, k, l) such that a[i] + a[j] + a[k] + a[l] = 0 public static int printAll(int[] a) { int N = a.length; int cnt = 0; for (int i = 0; i < N; i++) { for (int j = i+1; j < N; j++) { for (int k = j+1; k < N; k++) { for (int l = k+1; l < N; l++) { if (a[i] + a[j] + a[k] + a[l] == 0) { StdOut.println(a[i] + " " + a[j] + " " + a[k] + " " + a[l]); cnt ++; } } } } } return cnt; } // return number of distinct 4-tuples (i, j, k, l) such that a[i] + a[j] + a[k] + a[l] = 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++) { for (int k = j+1; k < N; k++) { for (int l = k+1; l < N; l++) { if (a[i] + a[j] + a[k] + a[l] == 0) { cnt++; } } } } } return cnt; } public static void main(String[] args) { StdIn.fromFile ("data/100ints.txt"); int[] a = StdIn.readAllInts(); int cnt = count(a); StdOut.println(cnt); if (cnt < 10) { printAll(a); } } } ```