POJ1850 Code 题解

#include<algorithm>
#include<cstdio>
#include<cmath>
#include<vector>
#include<cstring>
#include<iostream>
#include<queue>
#define W while
#define I inline
#define gc getchar
#define D isdigit(c=gc())
#define Cn const
#define pc(c) putchar((c))
#define LL long long
using namespace std;
I int read(){int x=0,f=1;char c;W(!D) f=c^'-'?1:-1;W(x=(x<<3)+(x<<1)+(c&15),D);return x*f;}
I void write(int x){x<0&&(pc('-'),x=-x),x<10?(pc(x+'0'),0):(write(x/10),pc(x%10+'0'),0);}
const int N=55;
int n,C[N][N],Ans;
char s[N];
I void init(){
for(int i=0;i<=53;i++) C[i][0]=C[i][i]=1;
for(int i=1;i<=53;i++)
for(int j=1;j<i;j++) C[i][j]=C[i-1][j]+C[i-1][j-1];
}
int main(){
init();cin>>s+1;n=strlen(s+1);
for(int i=1;i<n;i++)
if(s[i]>s[i+1]) return puts("0"),0;
for(int i=1;i<n;i++) Ans+=C[26][i];
for(int i=1;i<=n;i++)
for(int j=i==1?'a':s[i-1]+1;j<s[i];j++) Ans+=C['z'-j][n-i];
return write(Ans+1),pc('\n'),0;
}