给定一个包含N个整数的数组arr [] ，任务是打印k个索引的不同排列，以使这些索引处的值形成一个非递减序列。如果不可能，则打印-1 。
例子：
Input: arr[] = {1, 3, 3, 1}, k = 3
Output:
0 3 1 2
3 0 1 2
3 0 2 1
For every permutation, the values at the indices form the following sequence {1, 1, 3, 3}
Input: arr[] = {1, 2, 3, 4}, k = 3
Output: -1
There is only 1 non decreasing sequence possible {1, 2, 3, 4}.
方法：对给定的数组进行排序，并跟踪每个元素的原始索引。这给出了一个必需的排列。现在，如果任意两个连续元素相等，则可以交换它们以获得另一个排列。类似地，可以生成第三排列。
下面是上述方法的实现：
C++
// C++ implementation of the approach
#include
using namespace std;
int next_pos = 1;
// Utility function to print the original indices
// of the elements of the array
void printIndices(int n, pair a[])
{
for (int i = 0; i < n; i++)
cout << a[i].second << " ";
cout << endl;
}
// Function to print the required permutations
void printPermutations(int n, int a[], int k)
{
// To keep track of original indices
pair arr[n];
for (int i = 0; i < n; i++)
{
arr[i].first = a[i];
arr[i].second = i;
}
// Sort the array
sort(arr, arr + n);
// Count the number of swaps that can
// be made
int count = 1;
for (int i = 1; i < n; i++)
if (arr[i].first == arr[i - 1].first)
count++;
// Cannot generate 3 permutations
if (count < k) {
cout << "-1";
return;
}
for (int i = 0; i < k - 1; i++)
{
// Print the first permutation
printIndices(n, arr);
// Find an index to swap and create
// second permutation
for (int j = next_pos; j < n; j++)
{
if (arr[j].first == arr[j - 1].first)
{
swap(arr[j], arr[j - 1]);
next_pos = j + 1;
break;
}
}
}
// Print the last permuation
printIndices(n, arr);
}
// Driver code
int main()
{
int a[] = { 1, 3, 3, 1 };
int n = sizeof(a) / sizeof(a[0]);
int k = 3;
// Function call
printPermutations(n, a, k);
return 0;
} Java
// Java implementation of the approach
import java.util.*;
class GFG {
static int next_pos = 1;
static class pair {
int first, second;
pair()
{
first = 0;
second = 0;
}
}
// Utility function to print the original indices
// of the elements of the array
static void printIndices(int n, pair a[])
{
for (int i = 0; i < n; i++)
System.out.print(a[i].second + " ");
System.out.println();
}
static class sort implements Comparator
{
// Used for sorting in ascending order
public int compare(pair a, pair b)
{
return a.first < b.first ? -1 : 1;
}
}
// Function to print the required permutations
static void printPermutations(int n, int a[], int k)
{
// To keep track of original indices
pair arr[] = new pair[n];
for (int i = 0; i < n; i++)
{
arr[i] = new pair();
arr[i].first = a[i];
arr[i].second = i;
}
// Sort the array
Arrays.sort(arr, new sort());
// Count the number of swaps that can
// be made
int count = 1;
for (int i = 1; i < n; i++)
if (arr[i].first == arr[i - 1].first)
count++;
// Cannot generate 3 permutations
if (count < k)
{
System.out.print("-1");
return;
}
for (int i = 0; i < k - 1; i++)
{
// Print the first permutation
printIndices(n, arr);
// Find an index to swap and create
// second permutation
for (int j = next_pos; j < n; j++)
{
if (arr[j].first == arr[j - 1].first)
{
pair t = arr[j];
arr[j] = arr[j - 1];
arr[j - 1] = t;
next_pos = j + 1;
break;
}
}
}
// Print the last permuation
printIndices(n, arr);
}
// Driver code
public static void main(String arsg[])
{
int a[] = { 1, 3, 3, 1 };
int n = a.length;
int k = 3;
// Function call
printPermutations(n, a, k);
}
}
// This code is contributed by Arnab Kundu Python3
# Python 3 implementation of the approach
# Utility function to print the original
# indices of the elements of the array
def printIndices(n, a):
for i in range(n):
print(a[i][1], end=" ")
print("\n", end="")
# Function to print the required
# permutations
def printPermutations(n, a, k):
# To keep track of original indices
arr = [[0, 0] for i in range(n)]
for i in range(n):
arr[i][0] = a[i]
arr[i][1] = i
# Sort the array
arr.sort(reverse=False)
# Count the number of swaps that
# can be made
count = 1
for i in range(1, n):
if (arr[i][0] == arr[i - 1][0]):
count += 1
# Cannot generate 3 permutations
if (count < k):
print("-1", end="")
return
next_pos = 1
for i in range(k - 1):
# Print the first permutation
printIndices(n, arr)
# Find an index to swap and create
# second permutation
for j in range(next_pos, n):
if (arr[j][0] == arr[j - 1][0]):
temp = arr[j]
arr[j] = arr[j - 1]
arr[j - 1] = temp
next_pos = j + 1
break
# Print the last permuation
printIndices(n, arr)
# Driver code
if __name__ == '__main__':
a = [1, 3, 3, 1]
n = len(a)
k = 3
# Function call
printPermutations(n, a, k)
# This code is contributed by
# Surendra_GangwarC#
// C# implementation of the approach
using System;
using System.Collections;
using System.Collections.Generic;
class GFG {
static int next_pos = 1;
public class pair {
public int first, second;
public pair()
{
first = 0;
second = 0;
}
}
class sortHelper : IComparer
{
int IComparer.Compare(object a, object b)
{
pair first = (pair)a;
pair second = (pair)b;
return first.first < second.first ? -1 : 1;
}
}
// Utility function to print the original indices
// of the elements of the array
static void printIndices(int n, pair []a)
{
for (int i = 0; i < n; i++)
Console.Write(a[i].second + " ");
Console.WriteLine();
}
// Function to print the required permutations
static void printPermutations(int n, int []a, int k)
{
// To keep track of original indices
pair []arr = new pair[n];
for (int i = 0; i < n; i++)
{
arr[i] = new pair();
arr[i].first = a[i];
arr[i].second = i;
}
// Sort the array
Array.Sort(arr, new sortHelper());
// Count the number of swaps that can
// be made
int count = 1;
for (int i = 1; i < n; i++)
if (arr[i].first == arr[i - 1].first)
count++;
// Cannot generate 3 permutations
if (count < k)
{
Console.Write("-1");
return;
}
for (int i = 0; i < k - 1; i++)
{
// Print the first permutation
printIndices(n, arr);
// Find an index to swap and create
// second permutation
for (int j = next_pos; j < n; j++)
{
if (arr[j].first == arr[j - 1].first)
{
pair t = arr[j];
arr[j] = arr[j - 1];
arr[j - 1] = t;
next_pos = j + 1;
break;
}
}
}
// Print the last permuation
printIndices(n, arr);
}
// Driver code
public static void Main(string []args)
{
int []a = { 1, 3, 3, 1 };
int n = a.Length;
int k = 3;
// Function call
printPermutations(n, a, k);
}
}
// This code is contributed by rutvik_56.输出
0 3 1 2
3 0 1 2
3 0 2 1 时间复杂度： O(N log N + KN)
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