求范围 [1, N] 中 N 个数字的排列，使得 K 个数字的值与其索引相同

给定一个正整数N和一个整数K使得0 ≤ K ≤ N ，任务是找到 [1, N] 的任何排列A使得A _i = i的索引数正好是 K （基于 1索引）。如果不存在这样的排列，则打印-1 。

例子：

Input: N = 3, K = 1
Output: 1 3 2
Explanation: Consider the permutation A = [1, 3, 2]. We have A1=1, A2=3 and A3=2. 
So, this permutation has exactly 1 index such that A_i = i.

Input: N = 2, K = 1
Output: -1
Explanation : There are total 2 permutations of [1, 2] which are [1, 2] and [2, 1]. 
There are 2 indices in [1, 2] and 0 indices in [2, 1] for which A_i = i holds true. 
Thus, there doesn’t exist any permutation of [1, 2] with exactly 1 index i for which Ai=i holds true.

方法：可以使用贪心方法来解决任务。最初在它们的索引处精确地固定K个元素，然后随机地将NK个元素放在不同的位置。请按照以下步骤解决问题：

1. 以某种方式固定K个位置
2. 使剩余的NK数字脱臼
3. 将剩余元素循环移位一

下面是上述方法的实现：

C++

// C++ program for the above approach
#include 
using namespace std;
 
// Function to print permutation
void permutation(int N, int K)
{
    if (K == N) {
        for (int i = 1; i <= N; i++) {
            cout << i << ' ';
        }
        cout << '\n';
    }
    else if (K == N - 1) {
        cout << "-1" << '\n';
    }
    else {
        for (int i = 1; i <= K; i++) {
            cout << i << ' ';
        }
        for (int i = K + 2; i <= N; i++) {
            cout << i << ' ';
        }
        cout << K + 1 << '\n';
    }
}
 
// Driver Code
int main()
{
    int N = 3;
    int K = 1;
    permutation(N, K);
    return 0;
}

Java

// Java program to implement
// the above approach
import java.util.*;
public class GFG
{
 
// Function to print permutation
static void permutation(int N, int K)
{
    if (K == N) {
        for (int i = 1; i <= N; i++) {
            System.out.print(i + " ");
        }
        System.out.println();
    }
    else if (K == N - 1) {
        System.out.println("-1");
    }
    else {
        for (int i = 1; i <= K; i++) {
            System.out.print(i + " ");
        }
        for (int i = K + 2; i <= N; i++) {
            System.out.print(i + " ");
        }
        System.out.println(K + 1);
    }
}
 
// Driver Code
public static void main(String args[])
{
    int N = 3;
    int K = 1;
    permutation(N, K);
}
}
 
// This code is contributed by Samim Hossain Mondal.

Python3

# Python code for the above approach
 
# Function to print permutation
def permutation(N, K):
    if (K == N):
        for i in range(1, N + 1):
            print(i, end=" ")
        print('')
    elif (K == N - 1):
        print(-1)
    else:
        for i in range(1, K + 1):
            print(i, end=" ")
        for i in range(K + 2, N + 1):
            print(i, end=" ")
        print(K + 1)
 
# Driver Code
N = 3;
K = 1;
permutation(N, K);
 
# This code is contributed by Saurabh Jaiswal

C#

// C# program to implement
// the above approach
using System;
public class GFG {
 
  // Function to print permutation
  static void permutation(int N, int K)
  {
    if (K == N) {
      for (int i = 1; i <= N; i++) {
        Console.Write(i + " ");
      }
      Console.WriteLine();
    }
    else if (K == N - 1) {
      Console.WriteLine("-1");
    }
    else {
      for (int i = 1; i <= K; i++) {
        Console.Write(i + " ");
      }
      for (int i = K + 2; i <= N; i++) {
        Console.Write(i + " ");
      }
      Console.Write(K + 1);
    }
  }
 
  // Driver Code
  public static void Main()
  {
    int N = 3;
    int K = 1;
    permutation(N, K);
  }
}
 
// This code is contributed by ukasp.

Javascript

      // JavaScript code for the above approach
 
      // Function to print permutation
      function permutation(N, K) {
          if (K == N) {
              for (let i = 1; i <= N; i++) {
                  document.write(i + " ")
              }
              document.write('<br>')
          }
          else if (K == N - 1) {
              document.write(-1 + '<br>')
          }
          else {
              for (let i = 1; i <= K; i++) {
                  document.write(i + " ")
              }
              for (let i = K + 2; i <= N; i++) {
                  document.write(i + " ")
              }
              document.write(K + 1 + '<br>')
          }
      }
 
      // Driver Code
      let N = 3;
      let K = 1;
      permutation(N, K);
 
// This code is contributed by Potta Lokesh
  

输出

1 3 2

时间复杂度： O(N)
辅助空间： O(1)