Given a range [L, R] where L ? R, the task is to generate a random permutation of the sequence [L, L + 1, L + 2, …, R].
Examples:
Input: L = 5, R = 15
Output: 11 9 6 5 8 7 10 12 13 15 14
Input: L = 10, R = 20
Output: 16 14 11 10 13 12 15 17 18 20 19
Approach: We will use Divide and Conquer algorithm for our solution. We will create a global vector that will store random numbers generated by our recursive function generate_random_permutation().
We will pass two arguments L (start) and R (end) to our recursive function. Inside the function it will call another function give_random_number that will return a number between X and Y. Lets call it N. We will store this random number in our vector and then we will call generate_random_permutation() function recursively for range [L, N – 1] and then for range [N + 1, R].
If L becomes greater than R then we will return from the function without performing any task, as this is our base condition.
Below is the implementation of the above approach:
C++
// C++ implementation of the approach#include <bits/stdc++.h>using namespace std;// To store the random permutationvector<int> permutation;// Utility function to print// the generated permutationvoid printPermutation(){ for (auto i : permutation) cout << i << " ";}// Function to return a random// number between x and yint give_random_number(int l, int r){ int x = rand() % (r - l + 1) + l; return x;}// Recursive function to generate// the random permutationvoid generate_random_permutation(int l, int r){ // Base condition if (l > r) return; // Random number returned from the function int n = give_random_number(l, r); // Inserting random number in vector permutation.push_back(n); // Recursion call for [l, n - 1] generate_random_permutation(l, n - 1); // Recursion call for [n + 1, r] generate_random_permutation(n + 1, r);}// Driver codeint main(){ int l = 5; int r = 15; // Generate permutation generate_random_permutation(l, r); // Print the generated permutation printPermutation(); return 0;} |
Java
// Java implementation of the approachimport java.util.Vector;class GFG{// To store the random permutationstatic Vector<Integer> permutation = new Vector<>();// Utility function to print// the generated permutationstatic void printPermutation(){ permutation.stream().forEach((i) -> { System.out.print(i+" "); });}// Function to return a random// number between x and ystatic int give_random_number(int l, int r){ int x = (int) (Math.random()% (r - l + 1) + l); return x;}// Recursive function to generate// the random permutationstatic void generate_random_permutation(int l, int r){ // Base condition if (l > r) return; // Random number returned from the function int n = give_random_number(l, r); // Inserting random number in vector permutation.add(n); // Recursion call for [l, n - 1] generate_random_permutation(l, n - 1); // Recursion call for [n + 1, r] generate_random_permutation(n + 1, r);}// Driver codepublic static void main(String[] args){ int l = 5; int r = 15; // Generate permutation generate_random_permutation(l, r); // Print the generated permutation printPermutation();}}// This code has been contributed by 29AjayKumar |
Python3
# Python3 implementation of the approachimport random# To store the random permutationpermutation = []# Utility function to print# the generated permutationdef printPermutation() : for i in permutation: print(i, end = " ")# Function to return a random# number between x and ydef give_random_number(l, r) : x = random.randint(l, r) return x# Recursive function to generate# the random permutationdef generate_random_permutation(l, r) : # Base condition if (l > r) : return # Random number returned from the function n = give_random_number(l, r) # Inserting random number in vector permutation.append(n) # Recursion call for [l, n - 1] generate_random_permutation(l, n - 1) # Recursion call for [n + 1, r] generate_random_permutation(n + 1, r)# Driver codel = 5r = 15# Generate permutationgenerate_random_permutation(l, r)# Print the generated permutationprintPermutation()# This code is contributed by ihritik |
C#
// C# implementation of the approach using System;using System.Collections.Generic;class GFG{// To store the random permutationstatic List<int> permutation = new List<int>();// Utility function to print// the generated permutationstatic void printPermutation(){ foreach(int i in permutation) Console.Write(i+" ");}// Function to return a random// number between x and ystatic int give_random_number(int l, int r){ Random rnd = new Random(); int num = rnd.Next(l, r); int x = (int) (num % (r - l + 1) + l); return x;}// Recursive function to generate// the random permutationstatic void generate_random_permutation(int l, int r){ // Base condition if (l > r) return; // Random number returned from the function int n = give_random_number(l, r); // Inserting random number in vector permutation.Add(n); // Recursion call for [l, n - 1] generate_random_permutation(l, n - 1); // Recursion call for [n + 1, r] generate_random_permutation(n + 1, r);}// Driver codepublic static void Main(String[] args){ int l = 5; int r = 15; // Generate permutation generate_random_permutation(l, r); // Print the generated permutation printPermutation();}}/* This code contributed by PrinciRaj1992 */ |
PHP
<?php// PHP implementation of the approach// To store the random permutation$permutation = array();// Utility function to print// the generated permutationfunction printPermutation(){ global $permutation; foreach ($permutation as $i) echo $i . " ";}// Function to return a random// number between x and yfunction give_random_number($l, $r){ $x = rand() % ($r - $l + 1) + $l; return $x;}// Recursive function to generate// the random permutationfunction generate_random_permutation($l, $r){ global $permutation; // Base condition if ($l > $r) return; // Random number returned from the function $n = give_random_number($l, $r); // Inserting random number in vector array_push($permutation, $n); // Recursion call for [l, n - 1] generate_random_permutation($l, $n - 1); // Recursion call for [n + 1, r] generate_random_permutation($n + 1, $r);}// Driver code$l = 5;$r = 15;// Generate permutationgenerate_random_permutation($l, $r);// Print the generated permutationprintPermutation();// This code is contributed by mits?> |
Javascript
<script>// Javascript implementation of the approach// To store the random permutationvar permutation = [];// Utility function to print// the generated permutationfunction printPermutation(){ for (var i of permutation) document.write(i + " ");}// Function to return a random// number between x and yfunction give_random_number(l, r){ var x = Math.floor(Math.random() * l + r) % (r - l + 1) + l; return x;}// Recursive function to generate// the random permutationfunction generate_random_permutation(l, r){ // Base condition if (l > r) return; // Random number returned from the function var n = give_random_number(l, r); // Inserting random number in vector permutation.push(n); // Recursion call for [l, n - 1] generate_random_permutation(l, n - 1); // Recursion call for [n + 1, r] generate_random_permutation(n + 1, r);}// Driver codevar l = 5;var r = 15;// Generate permutationgenerate_random_permutation(l, r);// Print the generated permutationprintPermutation();// This code is contributed by rrrtnx.</script> |
Output:
11 9 6 5 8 7 10 12 13 15 14
Time Complexity: O(n)
Auxiliary Space: O(1)
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