POJ3332

http://acm.pku.edu.cn/JudgeOnline/problem?id=3332

 

实数解析，

关键是看懂这段定义：

Real numbers may have a decimal point, an exponent (starting with the character e or E), or both. Additionally, it has the usual collection of decimal digits. If there is a decimal point, there must be at least one digit on each side of the point. There may be a plus or minus sign in front of the number, or the exponent, or both (without any blank characters after the sign). Exponents are integers (not having decimal points).

 

关键点：如果有小数点者小数点两边至少都要有一个数。e和指数之间可以有 + — 或者都无。

Pattern pattern = Pattern.compile("\\d+(.\\d+)?([e|E]?|([e|E]([-|+]?\\d+)))?");

//Pattern pattern = Pattern.compile("\\d+(.\\d+)?([e|E]?|([e|E]([-|+]?\\d+)))?$"); 这种写法比前者慢

根据题意写出上述的表达式。

 

代码：

import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
	
	public static void main(String[] args) {
		//Scanner scn = new Scanner(Main.class.getResourceAsStream("in.dat"));
		PrintWriter out = new PrintWriter(System.out);
		Scanner scn = new Scanner(System.in);
		//Pattern pattern = Pattern.compile("\\s*(\\d+||\\d+.\\d{1,})(([e|E])?|([e|E]([-|+]?\\d+)))?");
		Pattern pattern = Pattern.compile("\\s*\\d+(.\\d+)?([e|E]?|([e|E]([-|+]?\\d+)))?");
		Matcher matcher;
		List<String> lines = new ArrayList<String>();
		int n = scn.nextInt();
		while(n-- != 0){
			lines.add(scn.next().trim());
		}
		n = lines.size();
		matcher = pattern.matcher(lines.get(0));
		for(int i = 0; i < n; i++){
			matcher.reset(lines.get(i));
			if(matcher.matches()){
				out.println("LEGAL");
			}else{
				out.println("ILLEGAL");
			}
		}
		out.flush();
	}

}

  

 还有一种方法是在读的时候就解析，但速度没有前者快，估计是io问题：

import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.regex.Pattern;

public class Main {
	
	public static void main(String[] args) {
		//Scanner scn = new Scanner(Main.class.getResourceAsStream("in.dat"));
		PrintWriter out = new PrintWriter(System.out);
		Scanner scn = new Scanner(System.in);
		//Pattern pattern = Pattern.compile("\\s*(\\d+||\\d+.\\d{1,})(([e|E])?|([e|E]([-|+]?\\d+)))?");
		Pattern pattern = Pattern.compile("\\s*\\d+(.\\d+)?([e|E]?|([e|E]([-|+]?\\d+)))?");
		List<String> lines = new ArrayList<String>();
		int n = scn.nextInt();
		scn.nextLine();
		//scn.useDelimiter(pattern);
		while(n-- != 0){
			if(scn.hasNext(pattern)){
				out.println("LEGAL");
			}else{
				out.println("ILLEGAL");
			}
			scn.nextLine();
			//System.out.println(scn.next(pattern));
			
			//lines.add(scn.next().trim());
		}
		/*n = lines.size();
		for(int i = 0; i < n; i++){
			if(pattern.matcher(lines.get(i)).matches()){
				out.println("LEGAL");
			}else{
				out.println("ILLEGAL");
			}
		}*/
		out.flush();
	}

}

 

 

PS：java速度用不如C 和 C++……