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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.clone();
  7.     }
  8.     public IntPermutation(int n) {
  9.         this.a = new int[n];
  10.         for (int i = 0; i < n; i++) a[i] = i;
  11.     }
  12.     public Iterator<int[]> iterator() {
  13.         return iterator_shared();
  14.     }
  15.     public Iterator<int[]> iterator_isolated() {
  16.         return a == null ? Collections.emptyIterator() : new Iterator<int[]>() {
  17.             private int[] a = IntPermutation.this.a.clone();
  18.             public boolean hasNext() {return a != null;}
  19.             public int[] next() {
  20.                 if (!hasNext()) throw new NoSuchElementException();
  21.                 int[] b = a.clone();
  22.                 a = next_or_null(a);
  23.                 return b;
  24.             }
  25.         };
  26.     }
  27.     public Iterator<int[]> iterator_shared() {
  28.         return a == null ? Collections.emptyIterator() : new Iterator<int[]>() {
  29.             private int[] a = IntPermutation.this.a.clone();
  30.             private int[] b = a;
  31.             public boolean hasNext() {
  32.                 if (a != null && b == null) b = a = next_or_null(a);
  33.                 return a != null;
  34.             }
  35.             public int[] next() {
  36.                 if (!hasNext()) throw new NoSuchElementException();
  37.                 b = null;
  38.                 return a;
  39.             }
  40.         };
  41.     }
  42.     public Stream<int[]> stream() {
  43.         return StreamSupport.stream(spliterator(), false);
  44.     }
  45.     private static int[] swap(int i, int j, int[] a) {
  46.         int t = a[i];a[i] = a[j];a[j] = t;
  47.         return a;
  48.     }
  49.     private static int[] rev(int b, int e, int[] a) {
  50.         for (e--; b < e; b++, e--) a = swap(b, e, a);
  51.         return a;
  52.     }
  53.     private static int[] next_or_null(int[] a) {
  54.         int e = a.length;
  55.         for (int i = e - 2, j = e - 1; 0 <= i; i--, j--)
  56.             if (a[i] < a[j])
  57.                 for (int k = e - 1; i < k; k--)
  58.                     if (a[i] < a[k])
  59.                         return rev(j, e, swap(i, k, a));
  60.         return null;
  61.     }
  62. }
  63. class Ideone {
  64.     private static int[] f(int[] a, int n) {
  65.         var it = new IntPermutation(a).iterator();
  66.         if (0 < n) for (int i = 1; it.hasNext(); i++) {
  67.             var b = it.next();
  68.             if (i == n) return b;
  69.         }
  70.         return null;
  71.     }
  72.     public static void main(String[] args) {
  73.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 1)));
  74.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 2)));
  75.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 3)));
  76.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 123456)));
  77.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 234567)));
  78.         System.out.println(Arrays.toString(f(new int[] {1,2,3,4,5,6,7,8,9}, 362880)));
  79.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 1)));
  80.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 2)));
  81.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 3)));
  82.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 123456)));
  83.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 234567)));
  84.         System.out.println(Arrays.toString(f(new int[] {1,1,1,2,2,2,3,3,3,4,4,4}, 369600)));
  85.     }
  86. }
  87.  
Success #stdin #stdout 0.14s 57268KB
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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/aKkfqN
language:
Java (HotSpot 12)
created:
23 days ago
visibility:
secret

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