POJ 1496

#include <iostream>
#include <string>
using namespace std;

int fac(int num);

int C(int n,int m);
int com( int n, int k );
int main()
{
    //freopen("acm.acm","r",stdin);
    string s;
    int sum;
    int j;
    int i;
//    cout<<com(4,2)<<endl;

    while(cin>>s)
    {
        sum = 0;
        for(i = 0; i < s.length()-1; ++ i)
        {
            sum += com(26,i+1);
        }
//        cout<<s<<endl;
//        cout<<"sum        "<<sum<<endl;
    
        //cout<<"len "<<s.length()<<endl;
        for(i = 0; i < s.length(); ++ i)
        {
            for(j = i+1; j < s.length(); ++ j)
            {
                if(s[i] >= s[j])
                {
                    break;
                }
            }
            if(j != s.length())
            {
                break;
            }
        }
        if(i != s.length())
        {
            cout<<0<<endl;
            continue;
        }
        for(i = 0; i < s.length(); ++ i)
        {
            if(i == 0)
            {
                j = 0;
            }
            else
            {
                j = s[i-1]-'a'+1;
            }
            for(; j < s[i]-'a'; ++ j)
            {
                sum += com(26-j-1,s.length()-i-1);
            }
        }
        cout<<sum+1<<endl;

    }
}

int C(int n,int m)
{
    return fac(n)/(fac(m)*fac(n-m));
}

int fac(int num)
{
    int i;
    int sum = 1;
    for(i = 1; i <= num; ++ i)
    {
        sum *= i;
    }
    return sum;
}

int com( int n, int k ) 
{

if ( k>0 )
{
   return com(n-1, k-1 ) * n / k;//组合公式
}
return 1;
}

 

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