poj 1850 Code

组合数学！！！

详情见：http://hi.baidu.com/lxyzmnwvhokptur/item/18c806469a668fe31e19bc1a#0

 1 #include<iostream>

 2 #include<stdio.h>

 3 #include<algorithm>

 4 #include<iomanip>

 5 #include<cmath>

 6 #include<cstring>

 7 #include<vector>

 8 #define ll __int64

 9 #define pi acos(-1.0)

10 #define MAX 50000

11 using namespace std;

12 char a[10];

13 int C(int n,int m){

14     int sum =1;

15     for (int i=n;i>n-m;i--) sum*=i;

16     for (int j=1;j<=m;j++) sum /=j;

17     return sum;

18 }

19 int main(){

20     int i,j,len,sum;

21     while(cin>>a){

22         sum=0;

23         len = strlen(a);

24         if (len == 1){

25             if (a[0]>='a'&&a[0]<='z')

26                 cout<<a[0]-'a'+1<<endl;

27             else cout<<0<<endl;

28             continue;

29         }

30         for (i=1;i<len;i++){

31             if (a[i]<=a[i-1])

32                 break;

33         }

34         if (i!=len){

35             cout<<0<<endl;

36             continue;

37         }

38         for (i=1;i<len;i++)

39             sum += C(26,i);

40         for (j=1;j<a[0]-'a'+1;j++)

41                 sum += C(26-j,len-1);

42         for (i=1;i<len;i++){

43             for (j=a[i-1]+2-'a';j<a[i]-'a'+1;j++)

44                 sum += C(26-j,len-i-1);

45         }

46         cout<<++sum<<endl;

47     }

48     return 0;

49 }