#include <bits/stdc++.h>
using namespace std;
string ran_shuff(string s)
{
	for (int i=0;i<s.size();i++)
	{
		swap(s[rand()%s.size()],s[rand()%s.size()]);
	}
	return s;
}
signed main()
{
    string s="";
    string cp=s;
    int c=0;
    for (int l=1;l<=10;l++)
    {
    	s="";
    	for (int i=1;i<=l;i++) s+=(i+'A')%26+65;
    	cp=s;
    	s=ran_shuff(s);
	    while (s!=cp)
		{
			s=ran_shuff(json);
			++c;
		}
		printf("length %d need %d times\n",l,c);
	}
}

c的期望值是多少?