hdu 1327 Definite Values

题目地址：

http://acm.hdu.edu.cn/showproblem.php?pid=1327

题目描述：

Definite Values

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 1202    Accepted Submission(s): 475

Problem Description

A common error in programming is to use variables that have not been initialized before. For example, in C and C++, all variables have an indefinite value after declaration - their value can be anything. Thus, the following program

main()
{
int x;
printf("%d\n",x);
}

could print any number. But even in languages such as Pascal, where all values are initialized to zero, it is useful to give variables definite values before using them, the avoid side effects when your code portion is placed into a different context.

Generally, the problem of deciding for a given program whether all variables have been assigned values before they are read out, is undecidable. But if you, as in this problem, consider only a sequence of assignments, the problem becomes solvable.

 

Input

The input contains several program parts. Each part starts with a number n on a line by itself, the number of lines in the program part. The following n lines contain each an assignment of the form "variable1 = variable2", where the variablei's are lower-case letters.

The input is terminated by a test case starting with n = 0.

 

Output

Assume that before the execution of the given program part, variable a has some definite value, while all other variables are undefined. You have to print the names of the varaibles which have a definite value after the execution of the program part. More specifically, format your output as follows.

For each program part in the input, first print the number of the program, as shown in the sample output. Then print a line containing the names of the variables which have a definite value after the execution of the given program part. Print them in alphabetically sorted order, and leave one blank after each variable name. If none of the variables has a definite value after the execution of the program part, print the word "none".

Print a blank line after each test case.

 

Sample Input

   
   
   
   

    
    
    
    4
b = a
c = d
d = b
e = f
1
a = b
0
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    Program #1
a b d 

Program #2
none
   
   
   
   

题意：

判断一段程序运行后，哪些变量是明确有定义的，哪些变量不是明确有定义的，初始化变量a是有定义的。

题解：

用map映射表，来实时记录变量中的值是否有明确定义，每走一行代码，映射表实时记录各个变量的情况。

注意：

这里hdu的oj的判断有问题，比如样例中输出: a b c

的格式是 a空格b空格c空格

而我第一次做的输出格式是a空格b空格c，结果得到了presentation error的错误。

也就是说一个样例输出一行字符，每个字符后面都必须跟一个空格字符，即使是最后一个字符。

代码：

#include<stdio.h>
#include<string.h>
int map_chars[300];//map['a'] = 1 is definite and 0 is indefinite
int n=0,cases=0;
char in_str[10];
int main()
{
    while(scanf("%d",&n)!=EOF&&n>0)
    {
        printf("Program #%d\n",++cases);
        memset(map_chars,0,sizeof(map_chars));
        map_chars['a']=1;
        for(int i=1;i<=n;i++)
        {
            fgets(in_str,10,stdin);
            while(in_str[0]=='\n') fgets(in_str,10,stdin);
            map_chars[in_str[0]]=map_chars[in_str[4]];
        }
        int flag=0,i=0;
        for(i='a';i<='z';i++)
        {
            if(map_chars[i]>0)
            {
                flag=1;
                printf("%c ",i);
            }
        }
        if(!flag) printf("none");
        printf("\n\n");
    }
    return(0);
}