poj 2503 Babelfish ----二分

Babelfish

Time Limit: 3000MS		Memory Limit: 65536K
Total Submissions: 22730		Accepted: 9756

Description

You have just moved from Waterloo to a big city. The people here speak an incomprehensible dialect of a foreign language. Fortunately, you have a dictionary to help you understand them.

Input

Input consists of up to 100,000 dictionary entries, followed by a blank line, followed by a message of up to 100,000 words. Each dictionary entry is a line containing an English word, followed by a space and a foreign language word. No foreign word appears
more than once in the dictionary. The message is a sequence of words in the foreign language, one word on each line. Each word in the input is a sequence of at most 10 lowercase letters.

Output

Output is the message translated to English, one word per line. Foreign words not in the dictionary should be translated as "eh".

Sample Input

dog ogday
cat atcay
pig igpay
froot ootfray
loops oopslay

atcay
ittenkay
oopslay

Sample Output

cat
eh
loops

题目大意: 一本方言字典，字典中可查到每个方言中单词对应的英文。 输入 英文单词，方言单词， 以一个空行表示字典输入结束。。。然后输入想要查找的方言单词，如果字典中有这个单词，输出英文单词。没有就输出eh。

思路：这道题一开始很容易想到hash，但hash 我现在还不太会。所以用了二分。hash的代码写了再贴。下面是二分查找的代码和思路。 这题学了 sscanf。 同时这道题 还有一个收获就是学会调用c语言库函数 bsearch。两段代码，一段没调用bsearch。一段是调用了bsearch的。关于qsort和 bsearch的细节博客中转载了两篇文章。 很有收获。

//Memory: 2516 KB		Time: 360 MS
//Language: C++		Result: Accepted

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
typedef struct w
{
char eng[12],dia[12];
}WORD;
WORD word[100100];
int cmp(const void *a,const void *b)   //qsort 的比较函数。
{
return strcmp( (*(WORD *)a).dia, (*(WORD *) b).dia);
}
int main()
{
//freopen("1.txt","r",stdin);
int i,len;
char temp[25];
for(i=0;;i++)
{
gets(temp);
if(temp[0]=='\0') break;
sscanf(temp,"%s%s",word[i].eng,word[i].dia);  //刚做此题 输入有点问题  但看了sscanf就很容易
}
len=i;
qsort(word,len,sizeof(word[0]),cmp);  //排序
char goal[12];
while(scanf("%s",goal)!=EOF)
{
int min=0,max=len,mid,ok=0;
while(min<=max)     //二分查找。
{
mid=(min+max)/2;
if(strcmp(word[mid].dia,goal)==0)
{
printf("%s\n",word[mid].eng) ;
ok=1;
break;
}
else if(strcmp(word[mid].dia,goal)>0) max=mid-1;
else min=mid+1;
}
if(!ok) printf("eh\n");
}
return 0;
}

// 学到了 bsearch 函数的调用
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
typedef struct w
{
char eng[12],dia[12];
}WORD;
WORD word[100100];
int qcmp(const void *a,const void *b)
{
return strcmp( (*(WORD *)a).dia, (*(WORD *) b).dia);
}
int bcmp(const void *c,const void *d)   //bsearch 的比较函数
{
return strcmp((char *)c,(* (WORD *)d).dia );
}
int main()
{
//freopen("1.txt","r",stdin);
int i,len;
char temp[25];
for(i=0;;i++)
{
gets(temp);
if(temp[0]=='\0') break;
sscanf(temp,"%s%s",word[i].eng,word[i].dia);
}
len=i;
qsort(word,len,sizeof(word[0]),qcmp);
char goal[12];
while(scanf("%s",goal)!=EOF)
{
WORD *p=(WORD *) bsearch(goal,word,len,sizeof(word[0]),bcmp);  //直接调用
if(!p) printf("eh\n");
else printf("%s\n",p->eng);
}
return 0;
}