一道有点意思的题目，主要是写起巨麻烦，先是判定，我很朴素，但是没问题。
然后，输出那一段，先写的WA#2，无语，改，然后再次WA#2，如此几次。
然后，到教室上数学课。最后重写输出的那一段，AC。
恩，无语。
CO
/*
PROGRAM: $PROGRAM
AUTHOR: Su Jiao
DATE: 2010-4-9
DESCRIPTION:
$DESCRIPTION
*/
#include <iostream>
using std::cin;
using std::cout;
#include <fstream>
using std::ifstream;
using std::ofstream;
#include <sstream>
using std::stringstream;
using std::endl;
#include <vector>
using std::vector;
#include <string>
using std::string;
#include <stack>
using std::stack;
#include <queue>
using std::queue;
using std::priority_queue;
#include <set>
using std::set;
#include <map>
using std::map;
using std::pair;
using std::make_pair;
#include <algorithm>
using std::sort;
#include <cassert>
//using std::assert;
#include <cmath>
using std::floor;
class Application
{
bool read(string& s,int& N)
{
s.clear();
char c;
while ((c=cin.get())!=’\n’) s.push_back(c);
if (s==“#”) return false;
cin>>N;
while ((c=cin.get())!=’\n’);
return true;
}
//<simple unsigned real number> ::=
// <unsigned integer number>
// |.<unsigned integer number>
// |<unsigned integer number>.<unsigned integer number>
bool simple_unsigned_real_number(const string& s)
{
if (unsigned_integer_number(s)) return true;
if (s.substr(0,1)==“.”
&&unsigned_integer_number(s.substr(1,s.length()-1)))
return true;
for (int i=1;i<s.length();i++)
if (unsigned_integer_number(s.substr(0,i))
&&s.substr(i,1)==“.”
&&unsigned_integer_number(s.substr(i+1,s.length()-i-1)))
return true;
return false;
}
//<simple real number> ::= <simple unsigned real number>
// |<sign><simple unsigned real number>
bool simple_real_number(const string& s)
{
if (simple_unsigned_real_number(s)) return true;
for (int i=1;i<s.length();i++)
if (sign(s.substr(0,i))
&&simple_unsigned_real_number(s.substr(i,s.length()-i)))
return true;
return false;
}
//<digit> ::= 0|1|2|3|4|5|6|7|8|9
bool digit(const string& s)
{
return s==“0”
||s==“1”
||s==“2”
||s==“3”
||s==“4”
||s==“5”
||s==“6”
||s==“7”
||s==“8”
||s==“9”;
}
//<unsigned integer number> ::= <digit>
// |<digit><unsigned integer number>
bool unsigned_integer_number(const string& s)
{
if (digit(s)) return true;
for (int i=1;i<s.length();i++)
if (digit(s.substr(0,i))
&&unsigned_integer_number(s.substr(i,s.length()-i)))
return true;
return false;
}
//<sign> ::= +|-
bool sign(const string& s)
{
return s==“+”||s==“-“;
}
//<integer number> ::= <unsigned integer number>
// |<sign><unsigned integer number>
bool integer_number(const string& s)
{
if (unsigned_integer_number(s)) return true;
for (int i=1;i<s.length();i++)
if (sign(s.substr(0,i))
&&unsigned_integer_number(s.substr(i,s.length()-i)))
return true;
return false;
}
//<exponent symbol> ::= e|E
bool exponent_symbol(const string& s)
{
return s==“e”||s==“E”;
}
//<exponent> ::= <exponent symbol><integer number>
bool exponent(const string& s)
{
for (int i=1;i<s.length();i++)
if (exponent_symbol(s.substr(0,i))
&&integer_number(s.substr(i,s.length()-i)))
return true;
return false;
}
//<real number> ::= <simple real number>
// |<simple real number><exponent>
bool real_number(const string& s)
{
if (simple_real_number(s)) return true;
for (int i=1;i<s.length();i++)
if (simple_real_number(s.substr(0,i))
&&exponent(s.substr(i,s.length()-i)))
return true;
return false;
}
void print_real_number(const string& s,int N)
{
static const int MAXLENGTH=200;
static const int MAXN=100;
int position_of_e=std::string::npos;
if (s.find(“e”)!=std::string::npos) position_of_e=s.find(“e”);
if (s.find(“E”)!=std::string::npos) position_of_e=s.find(“E”);
string simple_real_number_part;
int value_of_e;
if (position_of_e!=std::string::npos)
{
simple_real_number_part=s.substr(0,position_of_e);
stringstream
in(s.substr(position_of_e+1,s.length()-(position_of_e+1)));
double get;
in>>get;
if (get>MAXLENGTH) value_of_e=MAXLENGTH;
else if (get<-MAXLENGTH) value_of_e=-MAXLENGTH;
else value_of_e=floor(get+0.5);
}
else
{
simple_real_number_part=s;
value_of_e=0;
}
string integral_part;
string fractional_part;
int position_of_dot=simple_real_number_part.find(“.”);
if (position_of_dot!=std::string::npos)
{
integral_part=simple_real_number_part.substr(0,position_of_dot);
fractional_part=
simple_real_number_part
.substr(position_of_dot+1,
simple_real_number_part.length()-(position_of_dot+1));
}
else
integral_part=simple_real_number_part;
string flag;
if (integral_part[0]==’-‘)
{
flag=“-“;
integral_part.erase(0,1);
}
else if (integral_part[0]==’+’)
integral_part.erase(0,1);
do integral_part=“0”+integral_part;
while (int(integral_part.length())+value_of_e-1<=0);
do fractional_part=fractional_part+“0”;
while (int(fractional_part.length())-value_of_e-1<=0);
if (value_of_e<0)
{
fractional_part=
integral_part.substr(integral_part.length()+value_of_e,
-value_of_e)
+fractional_part;
integral_part.erase(integral_part.length()+value_of_e,
-value_of_e);
}
if (value_of_e>0)
{
integral_part=
integral_part
+fractional_part.substr(0,value_of_e);
fractional_part.erase(0,value_of_e);
}
bool equal_to_zero=true;
for (int i=0;i<integral_part.length();i++)
if (integral_part[i]!=’0′) equal_to_zero=false;
for (int i=0;i<fractional_part.length()&&i<N;i++)
if (fractional_part[i]!=’0′) equal_to_zero=false;
if (equal_to_zero) flag.clear();
while (integral_part[0]==’0’&&integral_part.length()>1)
integral_part.erase(0,1);
while (fractional_part.length()<MAXN)
fractional_part=fractional_part+“0”;
cout<<flag<<integral_part;
if (N)
{
cout<<“.”;
for (int i=0;i<N;i++)
cout<<fractional_part[i];
}
}
public:
Application()
{
}
int run()
{
string s;
int N;
while (read(s,N))
if (real_number(s))
{
print_real_number(s,N);
cout<<endl;
}
else cout<<“Not a floating point number”<<endl;
return 0;
}
};
int main()
{
Application app;
return app.run();
}