The prime circle of backtracking algorithm

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;namespaceseqlistsort{/// <summary>    /// <ather>    ///Lihonglin/// </ather>    /// <content>    ///The 20 numbers from 1 to 20 are placed in a ring, requiring the number of adjacent two and a prime. ///Analysis: Using backtracking algorithms to investigate all possible permutations/// </content>    /// </summary>    classPrimefor {Static intn = -; Static int[] A =New int[ -];//A array holds prime rings         Public Static voidinitprimefor () { for(inti =0; I < -; ++i) {A[i]= i +1; }        }         Public Static voidSwap (intIintj) {A[i]= A[i] + a[j]-(a[j] =A[i]); }        Static voidPrintresult () { for(inti =0; I < n; ++i) {Console.Write ("{0,-4}", A[i]);        } Console.WriteLine (); }        Static BOOLIsOK (intnum) {             for(inti =2; I <= (int) math.sqrt (num); ++i) {if(0= = num%i) {return false; }            }            return true; }         Public Static voidSearch (intk) {inti =0; if(k > N-1)//Judgment End Condition            {                if(IsOK (a[0] + a[n-1])) Printresult (); return; }            Else            {                 for(i = k; i < n; + +)i) {Swap (k, i); if(IsOK (A[k-1] +A[k])) {Search (k+1);//continue to explore                    }                    //BacktrackingSwap (k, i); }                           }        }    }}

The prime circle of backtracking algorithm