poj1496(组合数学)-与1850几乎一样

http://poj.org/problem?id=1496

Word Index

Time Limit: 1000MSMemory Limit: 10000KTotal Submissions: 3969Accepted: 2247

Description

Encoding schemes areoften used in situations requiring encryption or informationstorage/transmission economy. Here, we develop a simple encodingscheme that encodes particular types of words with five or fewer(lower case) letters as integers.

Consider the English alphabet {a,b,c,...,z}. Using this alphabet, aset of valid words are to be formed that are in a strictlexicographic order. In this set of valid words, the successiveletters of a word are in a strictly ascending order; that is, laterletters in a valid word are always after previous letters withrespect to their positions in the alphabet list {a,b,c,...,z}. Forexample,

abc aep gwz

are all valid three-letter words, whereas

aab are cat

are not.

For each valid word associate an integer which gives the positionof the word in the alphabetized list of words. That is:

    a -> 1
    b -> 2
    .
    .
    z -> 26
    ab -> 27
    ac -> 28
    .
    .
    az -> 51
    bc -> 52
    .
    .
    vwxyz -> 83681

Your program is to read a series of input lines. Each input linewill have a single word on it, that will be from one to fiveletters long. For each word read, if the word is invalid give thenumber 0. If the word read is valid, give the word's position indexin the above alphabetical list.

Input

The input consistsof a series of single words, one per line. The words are at leastone letter long and no more that five letters. Only the lower casealphabetic {a,b,...,z} characters will be used as input. The firstletter of a word will appear as the first character on an inputline.

The input will be terminated by end-of-file.

Output

The output is asingle integer, greater than or equal to zero (0) and less than orequal 83681. The first digit of an output value should be the firstcharacter on a line. There is one line of output for each inputline.

Sample Input

zacatvwxyz

Sample Output

261083681

Source

East Central North America 1995

详解参照上一篇文章poj1850。。

#include
#include
#include
using namespace std;
int c[27][27]={0};
void Init()
{
    for(inti=0;i<=26;i++)
    {
       for(int j=0;j<=i;j++)
       {
           if(j==0||i==j)
           {
               c[i][j]=1;
           }
           else c[i][j]=c[i-1][j-1]+c[i-1][j];
       }
    }
   c[0][0]=0;
   return;
}
int main()
{
    charstr[12];
   while(scanf("%s",str)!=EOF)
    {
       bool flag=false;
       Init();
       int len=strlen(str);
       for(int i=0;i<=len-2;i++)
       {
           if(str[i]>=str[i+1])
           {
               printf("0\n");
               flag=true;
               //return 0;
           }
       }
       int sum=0;
       if(flag==false)
       {

           for(int i=1;i
           {
               sum+=c[26][i];
               //printf()
           }
           for(int i=0;i
           {
               char ch=(i==0)?'a':str[i-1]+1;
               while(ch<=str[i]-1)
               {
                   sum+=c['z'-ch][len-i-1];
                   ch++;
               }
           }
           printf("%d\n",++sum);
       }
    }
    return0;
}