算法创作|蓝桥杯——排列序数问题解决方法

import java.util.Arrays;

import java.util.Scanner;

public class 排列序数 {

        public  static void main(String[] args) {

                 Scanner  in = new Scanner(System.in);

                 a  = in.next();

                 ch1  = a.toCharArray();

                 Arrays.sort(ch1);

                 n  = ch1.length;

                 vis  = new boolean[n];

                 ch2  = new char[n];

                 dfs(0);

                 System.out.println(ans);

        }

        static  char[] ch1;

        static  char[] ch2;

        static  boolean[] vis;

        static  int n;

        static  String a;

        static  int cnt=0,ans=0;

        static  void dfs(int m) {

                 if(ans>0)

                         return;

                 if(m>=n)  {

//                      System.out.println(new  String(ch2));

                         if(a.equals(new  String(ch2)))

                                  ans  = cnt;

                         cnt++;

                         return;

                 }

                 for(int  i=0;i<n;i++)

                         if(!vis[i])  {

                                  vis[i]  = true;

                                  ch2[m]  = ch1[i];

                                 dfs(m+1);

                                  vis[i]  = false;

                         }

        }

//     static  void swap(int i,int j) {

//             char  c = ch[i];

//             ch[i]  = ch[j];

//             ch[j]  = c;

//     }

}