644 - Immediate Decodability

    Uva644:

  Immediate Decodability 

An encoding of a set of symbols is said to be immediately decodable if no code for one symbol is the prefix of a code for another symbol. We will assume for this problem that all codes are in binary, that no two codes within a set of codes are the same, that each code has at least one bit and no more than ten bits, and that each set has at least two codes and no more than eight.

Examples: Assume an alphabet that has symbols {A, B, C, D}

The following code is immediately decodable:

A:01 B:10 C:0010 D:0000

but this one is not:

A:01 B:10 C:010 D:0000 (Note that A is a prefix of C)

Input 

Write a program that accepts as input a series of groups of records from a data file. Each record in a group contains a collection of zeroes and ones representing a binary code for a different symbol. Each group is followed by a single separator record containing a single 9; the separator records are not part of the group. Each group is independent of other groups; the codes in one group are not related to codes in any other group (that is, each group is to be processed independently).

Output 

For each group, your program should determine whether the codes in that group are immediately decodable, and should print a single output line giving the group number and stating whether the group is, or is not, immediately decodable.

The Sample Input describes the examples above.

Sample Input 

0110001000009011001000009

Sample Output 

Set 1 is immediately decodableSet 2 is not immediately decodable

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Miguel A. Revilla 
2000-01-17

之前没看懂题意连续WA了好几次了，题目大意是：给出一堆以9结尾的字符串集，判断是否Immediate Decodability，Immediate Decodability的定义是：集合中任意一个字符串不是其他字符串的前缀。

我的思路是：先给他们排序，拍完后只要判断前者是否后者的前缀，判断我是利用 strstr()函数，如果前面的字符串能在后面的字符串中找到且返回的后面字符串的首地址，说明前者是后者的前缀。

#include <iostream>#include <cstdio>#include <cstring>#include <cstdlib>using namespace std;int cmp(const void *a,const void *b){    return strcmp((char *)a,(char * )b);}int main(){//    freopen("a.txt","r",stdin);    char s[10][15];    int i,j,f,cas,c;    i=j=f=cas=0;    while((c=getchar())!=EOF)    {        if(c=='\n')        {            if(!f)            {                s[i++][j]='\0';                j=0;            }        }        else            if(c!='9')            {                f=0;                s[i][j++]=c;            }        else        {            f=1;            int q=0;            qsort(s,i,15*sizeof(char),cmp);//            for(int k=0;k<i;k++)//                cout<<s[k]<<endl;            for(int k=1;k<i;k++)            {                if(q)                    break;                for(int l=0;l<k;l++)                {                    if(s[k]-strstr(s[k],s[l])==0)                    {                        q=1;                        break;                    }                }            }//            printf("%d %d\n",i,q);            if(q)                printf("Set %d is not immediately decodable\n",++cas);            else                printf("Set %d is immediately decodable\n",++cas);            i=0;        }    }    return 0;}