A complete example of permutation and combination algorithm for C #

Permutation and combination is a common mathematical problem, this paper describes the method of C # Implementation of permutation combination algorithm in the form of a complete example. Share it for everyone's reference. Here's how:

First, the mathematical arrangement of the combination, can be expressed as: permutation P (n,r)

In fact, the implementation of the arrangement, the combination is realized, the combination of C (n,r) is P (n,r)/P (R,R), the implementation of this function is relatively simple recursive algorithm, but considering the performance of recursion, the following 2 kinds of non-recursive methods, the specific code is as follows

Using system;using System.collections.generic;namespace test{class Program {static void Main (string[] args) {      Console.WriteLine (P1 (6, 3));      Console.WriteLine (P2 (6, 3));    Console.WriteLine (C (6, 2)); }///<summary>/////</summary>//<param name= "N" ></param>//<para  M name= "R" ></param>///<returns></returns> static long P1 (int N, int r) {if (R > N || R <= 0 | |      N <= 0) throw new ArgumentException ("params invalid!");      Long T = 1;      int i = N;          while (I!=n-r) {try {checked {T *= i;        }} catch {throw new OverflowException ("Overflow happens!");      }-I.;    } return t; }///<summary>///Arrange Stack method///</summary>//<param name= "N" ></param>//<para M name= "R" ></param>//<returns></returns> static long P2 (int N, int r) {if (R > N | | R <= 0 | |      N <= 0) throw new ArgumentException ("Arguments invalid!");      stack<int> s = new stack<int> ();      Long iRlt = 1;      int t;      S.push (N);          while ((t = S.peek ()) = N-r) {try {checked {iRlt *= t;        }} catch {throw new OverflowException ("Overflow happens!");        } s.pop ();      S.push (t-1);    } return iRlt; }///<summary>////</summary>//<param name= "N" ></param>//<param NA  Me= "R" ></param>///<returns></returns> static long C (int N, int R) {return P1 (N, R)/    P1 (R, R); }  }}

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A complete example of permutation and combination algorithm for C #

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A complete example of permutation and combination algorithm for C #