Burnside’s Lemma is also sometimes known as orbit counting theorem. It is one of the results of group theory. It is used to count distinct objects with respect to symmetry. It basically gives us the formula to count the total number of combinations, where two objects that are symmetrical to each other with respect to rotation or reflection are counted as a single representative.
Therefore, Burnside Lemma’s states that total number of distinct object is:
where:
- c(k) is the number of combination that remains unchanged when Kth rotation is applied, and
- N is the total number of ways to change the position of N elements.
For Example:
Let us consider we have a necklace of N stones and we can color it with M colors. If two necklaces are similar after rotation then the two necklaces are considered to be similar and counted as one different combination. Now Let’s suppose we have N = 4 stones with M = 3 colors, then
Since we have N stones, therefore, we have N possible variations of each necklace by rotation:
Observations: There are N ways to change the position of the necklace as we can rotate it by 0 to N – 1 time.
- There are ways to color a necklace. If the number of rotations is 0, then all ways remain different.
- If the number of rotation is 1, then there are only M necklaces which will be different out of all ways.
- Generally, if the number of rotations is K, necklaces will remain the same out of all ways.
Therefore, for a total number of distinct necklaces of N stones after coloring with M colors is the summation of all the distinct necklaces at each rotation. It is given by:
Below is the implementation of the above approach:
C++
// C++ program for implementing the // Orbit counting theorem // or Burnside's Lemma #include <bits/stdc++.h> using namespace std; // Function to find result using // Orbit counting theorem // or Burnside's Lemma void countDistinctWays( int N, int M) { int ans = 0; // According to Burnside's Lemma // calculate distinct ways for each // rotation for ( int i = 0; i < N; i++) { // Find GCD int K = __gcd(i, N); ans += pow (M, K); } // Divide By N ans /= N; // Print the distinct ways cout << ans << endl; } // Driver Code int main() { // N stones and M colors int N = 4, M = 3; // Function call countDistinctWays(N, M); return 0; } |
Java
// Java program for implementing the // Orbit counting theorem // or Burnside's Lemma class GFG{ static int gcd( int a, int b) { if (a == 0 ) return b; return gcd(b % a, a); } // Function to find result using // Orbit counting theorem // or Burnside's Lemma static void countDistinctWays( int N, int M) { int ans = 0 ; // According to Burnside's Lemma // calculate distinct ways for each // rotation for ( int i = 0 ; i < N; i++) { // Find GCD int K = gcd(i, N); ans += Math.pow(M, K); } // Divide By N ans /= N; // Print the distinct ways System.out.print(ans); } // Driver Code public static void main(String []args) { // N stones and M colors int N = 4 , M = 3 ; // Function call countDistinctWays(N, M); } } // This code is contributed by rutvik_56 |
Python3
# Python3 program for implementing the # Orbit counting theorem # or Burnside's Lemma from math import gcd # Function to find result using # Orbit counting theorem # or Burnside's Lemma def countDistinctWays(N, M): ans = 0 ; # According to Burnside's Lemma # calculate distinct ways for each # rotation for i in range (N): # Find GCD K = gcd(i, N); ans + = pow (M, K); # Divide By N ans / / = N; # Print the distinct ways print (ans); # Driver Code # N stones and M colors N = 4 M = 3 ; # Function call countDistinctWays(N, M); # This code is contributed by phasing17 |
C#
// C# program for implementing the // Orbit counting theorem // or Burnside's Lemma using System; class GFG { static int gcd( int a, int b) { if (a == 0) return b; return gcd(b % a, a); } // Function to find result using // Orbit counting theorem // or Burnside's Lemma static void countDistinctWays( int N, int M) { int ans = 0; // According to Burnside's Lemma // calculate distinct ways for each // rotation for ( int i = 0; i < N; i++) { // Find GCD int K = gcd(i, N); ans += ( int )Math.Pow(M, K); } // Divide By N ans /= N; // Print the distinct ways Console.Write(ans); } // Driver Code public static void Main( string []args) { // N stones and M colors int N = 4, M = 3; // Function call countDistinctWays(N, M); } } // This code is contributed by pratham76 |
Javascript
<script> // Javascript <script> // Javascript program for implementing the // Orbit counting theorem // or Burnside's Lemma function gcd(a, b) { if (a == 0) return b; return gcd(b % a, a); } // Function to find result using // Orbit counting theorem // or Burnside's Lemma function countDistinctWays(N, M) { let ans = 0; // According to Burnside's Lemma // calculate distinct ways for each // rotation for (let i = 0; i < N; i++) { // Find GCD let K = gcd(i, N); ans += Math.pow(M, K); } // Divide By N ans /= N; // Print the distinct ways document.write(ans); } // Driver Code // N stones and M colors let N = 4, M = 3; // Function call countDistinctWays(N, M); </script> |
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