Given two numbers, n >= 0 and 0 <= k <= n, count the number of derangements with k fixed points.
Examples:
Input : n = 3, k = 0
Output : 2
Since k = 0, no point needs to be on its
original position. So derangements
are {3, 1, 2} and {2, 3, 1}
Input : n = 3, k = 1
Output : 3
Since k = 1, one point needs to be on its
original position. So partial derangements
are {1, 3, 2}, {3, 2, 1} and {2, 1, 3}
Input : n = 7, k = 2
Output : 924
In combinatorial mathematics, the rencontres number< or D(n, k) represents count of partial derangements.
The recurrence relation to find Rencontres Number Dn, k:
D(0, 0) = 1
D(0, 1) = 0
D(n+2, 0) = (n+1) * (D(n+1, 0) + D(n, 0))
D(n, k) = nCk * D(n-k, 0))
Given the two positive integer n and k. The task is find rencontres number D(n, k) for giver n and k.
Below is Recursive solution of this approach:
C++
// Recursive CPP program to find n-th Rencontres // Number #include <bits/stdc++.h> using namespace std; // Returns value of Binomial Coefficient C(n, k) int binomialCoeff(int n, int k) { // Base Cases if (k == 0 || k == n) return 1; // Recurrence relation return binomialCoeff(n - 1, k - 1) + binomialCoeff(n - 1, k); } // Return Recontres number D(n, m) int RencontresNumber(int n, int m) { // base condition if (n == 0 && m == 0) return 1; // base condition if (n == 1 && m == 0) return 0; // base condition if (m == 0) return (n - 1) * (RencontresNumber(n - 1, 0) + RencontresNumber(n - 2, 0)); return binomialCoeff(n, m) * RencontresNumber(n - m, 0); } // Driver Program int main() { int n = 7, m = 2; cout << RencontresNumber(n, m) << endl; return 0; } |
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Java
// Recursive Java program to find n-th Rencontres // Number import java.io.*; class GFG { // Returns value of Binomial Coefficient // C(n, k) static int binomialCoeff(int n, int k) { // Base Cases if (k == 0 || k == n) return 1; // Recurrence relation return binomialCoeff(n - 1, k - 1) + binomialCoeff(n - 1, k); } // Return Recontres number D(n, m) static int RencontresNumber(int n, int m) { // base condition if (n == 0 && m == 0) return 1; // base condition if (n == 1 && m == 0) return 0; // base condition if (m == 0) return (n - 1) * (RencontresNumber(n - 1, 0) + RencontresNumber(n - 2, 0)); return binomialCoeff(n, m) * RencontresNumber(n - m, 0); } // Driver Program public static void main(String[] args) { int n = 7, m = 2; System.out.println(RencontresNumber(n, m)); } } // This code is contributed by vt_m. |
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Python3
# Recursive CPP program to find # n-th Rencontres Number # Returns value of Binomial Coefficient C(n, k) def binomialCoeff(n, k): # Base Cases if (k == 0 or k == n): return 1 # Recurrence relation return (binomialCoeff(n - 1, k - 1) + binomialCoeff(n - 1, k)) # Return Recontres number D(n, m) def RencontresNumber(n, m): # base condition if (n == 0 and m == 0): return 1 # base condition if (n == 1 and m == 0): return 0 # base condition if (m == 0): return ((n - 1) * (RencontresNumber(n - 1, 0) + RencontresNumber(n - 2, 0))) return (binomialCoeff(n, m) * RencontresNumber(n - m, 0)) # Driver Program n = 7; m = 2print(RencontresNumber(n, m)) # This code is contributed by Smitha Dinesh Semwal. |
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C#
// Recursive C# program to find n-th Rencontres // Number using System; class GFG { // Returns value of Binomial Coefficient // C(n, k) static int binomialCoeff(int n, int k) { // Base Cases if (k == 0 || k == n) return 1; // Recurrence relation return binomialCoeff(n - 1, k - 1) + binomialCoeff(n - 1, k); } // Return Recontres number D(n, m) static int RencontresNumber(int n, int m) { // base condition if (n == 0 && m == 0) return 1; // base condition if (n == 1 && m == 0) return 0; // base condition if (m == 0) return (n - 1) * (RencontresNumber(n - 1, 0) + RencontresNumber(n - 2, 0)); return binomialCoeff(n, m) * RencontresNumber(n - m, 0); } // Driver Program public static void Main() { int n = 7, m = 2; Console.Write(RencontresNumber(n, m)); } } // This code is contributed by // Smitha Dinesh Semwal |
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PHP
<?php // Recursive PHP program to // find n-th Rencontres // Number // Returns value of Binomial // Coefficient C(n, k) function binomialCoeff($n, $k) { // Base Cases if ($k == 0 || $k == $n) return 1; // Recurrence relation return binomialCoeff($n - 1,$k - 1) + binomialCoeff($n - 1, $k); } // Return Recontres number D(n, m) function RencontresNumber($n, $m) { // base condition if ($n == 0 && $m == 0) return 1; // base condition if ($n == 1 && $m == 0) return 0; // base condition if ($m == 0) return ($n - 1) * (RencontresNumber($n - 1, 0) + RencontresNumber($n - 2, 0)); return binomialCoeff($n, $m) * RencontresNumber($n - $m, 0); } // Driver Code $n = 7; $m = 2; echo RencontresNumber($n, $m),"\n"; // This code is contributed by ajit. ?> |
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Output:
924
Below is the implementation using Dynamic Programming:
C++
// DP based CPP program to find n-th Rencontres // Number #include <bits/stdc++.h> using namespace std; #define MAX 100 // Fills table C[n+1][k+1] such that C[i][j] // represents table of binomial coefficient // iCj int binomialCoeff(int C[][MAX], int n, int k) { // Calculate value of Binomial Coefficient // in bottom up manner for (int i = 0; i <= n; i++) { for (int j = 0; j <= min(i, k); j++) { // Base Cases if (j == 0 || j == i) C[i][j] = 1; // Calculate value using previously // stored values else C[i][j] = C[i - 1][j - 1] + C[i - 1][j]; } } } // Return Recontres number D(n, m) int RencontresNumber(int C[][MAX], int n, int m) { int dp[n+1][m+1] = { 0 }; for (int i = 0; i <= n; i++) { for (int j = 0; j <= m; j++) { if (j <= i) { // base case if (i == 0 && j == 0) dp[i][j] = 1; // base case else if (i == 1 && j == 0) dp[i][j] = 0; else if (j == 0) dp[i][j] = (i - 1) * (dp[i - 1][0] + dp[i - 2][0]); else dp[i][j] = C[i][j] * dp[i - j][0]; } } } return dp[n][m]; } // Driver Program int main() { int n = 7, m = 2; int C[MAX][MAX]; binomialCoeff(C, n, m); cout << RencontresNumber(C, n, m) << endl; return 0; } |
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Java
// DP based Java program to find n-th Rencontres // Number import java.io.*; class GFG { static int MAX = 100; // Fills table C[n+1][k+1] such that C[i][j] // represents table of binomial coefficient // iCj static void binomialCoeff(int C[][], int n, int k) { // Calculate value of Binomial Coefficient // in bottom up manner for (int i = 0; i <= n; i++) { for (int j = 0; j <= Math.min(i, k); j++) { // Base Cases if (j == 0 || j == i) C[i][j] = 1; // Calculate value using previously // stored values else C[i][j] = C[i - 1][j - 1] + C[i - 1][j]; } } } // Return Recontres number D(n, m) static int RencontresNumber(int C[][], int n, int m) { int dp[][] = new int[n + 1][m + 1]; for (int i = 0; i <= n; i++) { for (int j = 0; j <= m; j++) { if (j <= i) { // base case if (i == 0 && j == 0) dp[i][j] = 1; // base case else if (i == 1 && j == 0) dp[i][j] = 0; else if (j == 0) dp[i][j] = (i - 1) * (dp[i - 1][0] + dp[i - 2][0]); else dp[i][j] = C[i][j] * dp[i - j][0]; } } } return dp[n][m]; } // Driver Program public static void main(String[] args) { int n = 7, m = 2; int C[][] = new int[MAX][MAX]; binomialCoeff(C, n, m); System.out.println(RencontresNumber(C, n, m)); } } // This code is contributed by vt_m. |
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Python 3
# DP based Python 3 program to find n-th # Rencontres Number MAX = 100 # Fills table C[n+1][k+1] such that C[i][j] # represents table of binomial coefficient # iCj def binomialCoeff(C, n, k) : # Calculate value of Binomial Coefficient # in bottom up manner for i in range(0, n + 1) : for j in range(0, min(i, k) + 1) : # Base Cases if (j == 0 or j == i) : C[i][j] = 1 # Calculate value using previously # stored values else : C[i][j] = (C[i - 1][j - 1] + C[i - 1][j]) # Return Recontres number D(n, m) def RencontresNumber(C, n, m) : w, h = m+1, n+1 dp= [[0 for x in range(w)] for y in range(h)] for i in range(0, n+1) : for j in range(0, m+1) : if (j <= i) : # base case if (i == 0 and j == 0) : dp[i][j] = 1 # base case elif (i == 1 and j == 0) : dp[i][j] = 0 elif (j == 0) : dp[i][j] = ((i - 1) * (dp[i - 1][0] + dp[i - 2][0])) else : dp[i][j] = C[i][j] * dp[i - j][0] return dp[n][m] # Driver Program n = 7m = 2C = [[0 for x in range(MAX)] for y in range(MAX)] binomialCoeff(C, n, m) print(RencontresNumber(C, n, m)) # This code is contributed by Nikita Tiwari. |
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C#
// DP based C# program // to find n-th Rencontres // Number using System; class GFG { static int MAX = 100; // Fills table C[n+1][k+1] // such that C[i][j] // represents table of // binomial coefficient iCj static void binomialCoeff(int [,]C, int n, int k) { // Calculate value of // Binomial Coefficient // in bottom up manner for (int i = 0; i <= n; i++) { for (int j = 0; j <= Math.Min(i, k); j++) { // Base Cases if (j == 0 || j == i) C[i,j] = 1; // Calculate value using // previously stored values else C[i, j] = C[i - 1, j - 1] + C[i - 1, j]; } } } // Return Recontres // number D(n, m) static int RencontresNumber(int [,]C, int n, int m) { int [,]dp = new int[n + 1, m + 1]; for (int i = 0; i <= n; i++) { for (int j = 0; j <= m; j++) { if (j <= i) { // base case if (i == 0 && j == 0) dp[i, j] = 1; // base case else if (i == 1 && j == 0) dp[i, j] = 0; else if (j == 0) dp[i, j] = (i - 1) * (dp[i - 1, 0] + dp[i - 2, 0]); else dp[i, j] = C[i, j] * dp[i - j, 0]; } } } return dp[n, m]; } // Driver Code static public void Main () { int n = 7, m = 2; int [,]C = new int[MAX, MAX]; binomialCoeff(C, n, m); Console.WriteLine(RencontresNumber(C, n, m)); } } // This code is contributed // by akt_mit |
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PHP
<?php // DP based PHP program to find n-th Rencontres // Number $MAX=100; // Fills table C[n+1][k+1] such that C[i][j] // represents table of binomial coefficient // iCj function binomialCoeff(&$C, $n, $k) { // Calculate value of Binomial Coefficient // in bottom up manner for ($i = 0; $i <= $n; $i++) { for ($j = 0; $j <= min($i, $k); $j++) { // Base Cases if ($j == 0 || $j == $i) $C[$i][$j] = 1; // Calculate value using previously // stored values else $C[$i][$j] = $C[$i - 1][$j - 1] + $C[$i - 1][$j]; } } } // Return Recontres number D(n, m) function RencontresNumber($C, $n, $m) { $dp=array_fill(0,$n+1,array_fill(0,$m+1,0)); for ($i = 0; $i <= $n; $i++) { for ($j = 0; $j <= $m; $j++) { if ($j <= $i) { // base case if ($i == 0 && $j == 0) $dp[$i][$j] = 1; // base case else if ($i == 1 && $j == 0) $dp[$i][$j] = 0; else if ($j == 0) $dp[$i][$j] = ($i - 1) * ($dp[$i - 1][0] + $dp[$i - 2][0]); else $dp[$i][$j] = $C[$i][$j] * $dp[$i - $j][0]; } } } return $dp[$n][$m]; } // Driver Program $n = 7; $m = 2; $C=array(array()); binomialCoeff($C, $n, $m); echo RencontresNumber($C, $n, $m); // This code is contributed // by mits ?> |
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Output:
924
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