A detailed description of C # permutations and combinations

The concept of permutation combinations

Arrange: Remove m (m≤n) elements from n different elements, in a certain order, called a permutation of m elements from n elements (arrangement).

Combination: from m different elements, any n (n≤m) element is a group called a combination of n elements taken from m different elements.

Permutation combination Implementation code

The previous project did a waterway path planning when using the arranged data structure. The number of combinations of the different sequences of M points in any n points.

The optimal path is thus obtained. The following is an algorithm that does not know where to look for permutation combinations.

public class Permutationandcombination<t> {//<summary>///Exchange two variables//</summary>//<param name= " A "> Variable 1</param>//<param name=" B "> variable 2</param> public static void Swap (Ref t A, ref T B) {T temp = a ; A = b; b = temp; }///<summary>///recursive algorithm for array combination (private Member)///</summary>//<param name= "List" > Return paradigm </param>//< param name= "T" > Array </param>//<param name= "n" > Auxiliary variable </param>//<param name= "M" > Auxiliary variable </ param>//<param name= "B" > Auxiliary array </param>///<param Name= "M" > Auxiliary variable m</param> private static  void Getcombination (ref list<t[]> List, t[] T, int n, int m, int[] b, int m) {for (int i = n; i >= m; i--) {b[m -1] = i-1; if (M > 1) {getcombination (ref list, T, I-1, m-1, B, M);} else {if (list = = null) {list = new list<t[]> () ; } t[] temp = new T[m]; for (int j = 0; J < B.length; J + +) {Temp[j] = T[b[j]];} list. ADD (temp); }}}///<summary&Gt Recursive algorithm permutation (private member)///</summary>//<param name= "List" > returned list </param>//<param name= "T" > the array to be evaluated and lt;/param>//<param name= "StartIndex" > Starting label </param>//<param name= "EndIndex" > End label </param  > private static void Getpermutation (ref list<t[]> List, t[] T, int startIndex, int endIndex) {if (StartIndex = = EndIndex) {if (list = = null) {list = new list<t[]> ();} t[] temp = new T[t.length]; T.copyto (temp, 0); List. ADD (temp); } else {for (int i = startIndex; I <= endIndex; i++) {Swap (ref T[startindex], ref t[i]); Getpermutation (ref list, T, StartIndex + 1, endIndex); Swap (ref T[startindex], ref t[i]); }}}///<summary>//For the arrangement from the starting label to the end label, the remaining elements are unchanged///</summary>//<param name= "T" > The array </param>// <param name= "StartIndex" > Start label </param>//<param name= "EndIndex" > End label </param>//< Returns> type </returns> public static list<t[]> getpermutation (t[] T, I, from the starting label to the end label arrangementNT StartIndex, int endIndex) {if (StartIndex < 0 | | EndIndex > T.LENGTH-1) {return null;} list<t[]> list = new list<t[]> (); Getpermutation (ref list, T, StartIndex, EndIndex); return list; }///<summary>///Returns the full arrangement of all elements of the array///</summary>//<param name= "T" > The array </param>//<returns&  gt; full-aligned paradigm </returns> public static list<t[]> getpermutation (t[] t) {return getpermutation (T, 0, t.length-1); }///<summary>//To arrange the arrangement of n elements in the array///</summary>//<param name= "T" > The array </param>//<param Nam E= "n" > number of Elements </param>//<returns> arrangement of n elements in arrays </returns> public static list<t[]> Getpermutation (t[] T, int n) {if (n > T.length) {return null;} list<t[]> list = new list<t[]> (); list<t[]> C = getcombination (T, N); for (int i = 0; i < C.count; i++) {list<t[]> L = new list<t[]> (); Getpermutation (ref L, C[i], 0, n-1); List. AddRange (l); } return list; }//<summary>////Find a combination of n elements in an array///</summary>//<param name= "T" > Array </param>//<param name= "n" > Number of elements </param>//<returns> combination of n elements in an array of paradigms </returns> public static list<t[]> getcombination (t[] T, int n) {if (T.length < n) {return null;} int[] temp = new Int[n]; list<t[]> list = new list<t[]> (); Getcombination (ref list, T, T.length, N, temp, n); return list; } }

Combinatorial: Find a combination of any 3 numbers in 5 numbers

static void Main (string[] args) {int[] intarr = new int[] {1, 2, 3, 4, 5};//integer array list<int[]> listcombination = Perm Utationandcombination<int>. Getcombination (Intarr, 3); For all 3-3 combinations of foreach (int[] arr in listcombination) {foreach (int item in arr) {Console.Write (item + "");} Console.WriteLine ("");} Console.readkey ();}

Arrange: 5 numbers to take 3 arbitrary arrangement

I

nt[] intarr = new int[] {1, 2, 3, 4, 5}; Integer array list<int[]> listcombination = Permutationandcombination<int>. Getpermutation (Intarr, 3); Ask for all 5 fetch 3 to arrange foreach (int[] arr in listcombination) {foreach (int item in arr) {Console.Write (item + "");} Console.WriteLine ("");}

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