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  1. import java.util.*;
  2. import java.util.stream.*;
  3. class IntPermutation implements Iterable<int[]> {
  4.     private final int[] a;
  5.     public IntPermutation(int[] a) {
  6.         this.a = a;
  7.     }
  8.     public Iterator<int[]> iterator() {
  9.         return a == null ? Collections.emptyIterator() : new Iterator<int[]>() {
  10.             private int[] a = IntPermutation.this.a.clone();
  11.             public boolean hasNext() {return a != null;}
  12.             public int[] next() {
  13.                 if (!hasNext()) throw new NoSuchElementException();
  14.                 int[] b = a.clone();
  15.                 a = next_or_null(a);
  16.                 return b;
  17.             }
  18.         };
  19.     }
  20.     public Stream<int[]> stream() {
  21.         return StreamSupport.stream(spliterator(), false);
  22.     }
  23.     private static int[] swap(int i, int j, int[] a) {
  24.         int t = a[i];a[i] = a[j];a[j] = t;
  25.         return a;
  26.     }
  27.     private static int[] rev(int b, int e, int[] a) {
  28.         for (e--; b < e; b++, e--) a = swap(b, e, a);
  29.         return a;
  30.     }
  31.     private static int[] next_or_null(int[] a) {
  32.         int e = a.length;
  33.         for (int i = e - 2, j = e - 1; 0 <= i; i--, j--)
  34.             if (a[i] < a[j])
  35.                 for (int k = e - 1; i < k; k--)
  36.                     if (a[i] < a[k])
  37.                         return rev(j, e, swap(i, k, a));
  38.         return null;
  39.     }
  40. }
  41. class Ideone {
  42.     private static int[] f(int[] a, int n) {
  43.         var it = new IntPermutation(a).iterator();
  44.         for (int i = 1; i <= n && it.hasNext(); i++) {
  45.             var b = it.next();
  46.             if (i == n) return b;
  47.         }
  48.         return null;
  49.     }
  50.     public static void main(String[] args) {
  51.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 1)));
  52.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 2)));
  53.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 3)));
  54.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 123456)));
  55.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 234567)));
  56.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 362880)));
  57.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 1)));
  58.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 2)));
  59.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 3)));
  60.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 123456)));
  61.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 234567)));
  62.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 369600)));
  63.     }
  64. }
  65.  
Success #stdin #stdout 0.18s 121412KB
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stdin
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Standard input is empty
stdout
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[1, 2, 3, 4, 5, 6, 7, 8, 9]
[1, 2, 3, 4, 5, 6, 7, 9, 8]
[1, 2, 3, 4, 5, 6, 8, 7, 9]
[4, 1, 6, 5, 8, 9, 7, 3, 2]
[6, 8, 4, 7, 5, 3, 2, 1, 9]
[9, 8, 7, 6, 5, 4, 3, 2, 1]
[1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4]
[1, 1, 1, 2, 2, 2, 3, 3, 4, 3, 4, 4]
[1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 3, 4]
[2, 2, 2, 3, 3, 1, 4, 3, 4, 1, 1, 4]
[3, 2, 4, 4, 2, 4, 3, 3, 1, 1, 1, 2]
[4, 4, 4, 3, 3, 3, 2, 2, 2, 1, 1, 1]
https://ideone.com/NRTZpa
language:
Java (HotSpot 12)
created:
27 days ago
visibility:
secret

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