Complicated Expressions

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#1 futura91

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• Posts: 12
• Joined: 27-July 07

Complicated Expressions

Posted 18 August 2007 - 08:35 PM

i've got one last assignment:

Machine Problem 4
Complicated Expressions
Filename: MP4FamilyName.java
Deadline: August 20, 2007 12:00 NN
Input: inMP4.txt
Output: console
The most important activity of ACM is the GSM network. As the mobile phone operator, ACM must build its own transmitting stations. It is very important to compute the exact behavior of electro-magnetic waves. Unfortunately, prediction of electro-magnetic fields is a very complex task and the formulas describing them are very long and hard-to-read. For example, below are the Maxwell's Equations describing the basic laws of electrical engineering.
ACM has designed its own computer system that can make some field computations and produce results in the form of mathematic expressions. Unfortunately, by generating the expression in several steps, there are always some unneeded parentheses inside the expression. Your task is to take these partial results and make them "nice" by removing all unnecessary parentheses.
Input
There is a single positive integer T on the first line of input. It stands for the number of expressions to follow. Each expression consists of a single line containing only lowercase letters, operators (+, -, *, /) and parentheses (( and )). The letters are variables that can have any value, operators and parentheses have their usual meaning. Multiplication and division have higher priority then subtraction and addition. All operations with the same priority are computed from left to right (operators are leftassociative). There are no spaces inside the expressions. No input line contains more
than 250 characters.
Output
Print a single line for every expression. The line must contain the same expression with unneeded parentheses removed. You must remove as many parentheses as possible without changing the semantics of the expression. The semantics of the expression is considered the same if and only if any of the following conditions hold:
o The ordering of operations remains the same. That means "(a+B)+c" is the same
as "a+b+c", and "a+(b/c)" is the same as "a+b/c".
o The order of some operations is swapped but the result remains unchanged with respect to the addition and multiplication associativity. That means "a+(b+c)" and "(a+B)+c" are the same. We can also combine addition with subtraction and multiplication with division, if the subtraction or division is the second operation. For example, "a+(b-c)" is the same as "a+b-c".
o You cannot use any other laws, namely you cannot swap left and right operands and you cannot replace "a-(b-c)" with "a-b+c".
Sample Input
8
(a+(b*c))
((a+B)*c)
(a*(b*c))
(a*(b/c)*d)
((a/(b/c))/d)
((x))
(a+B)-(c-d)-(e/f)
(a+B)+(c-d)-(e+f)
Sample Output
a+b*c
(a+B)*c
a*b*c
a*b/c*d
a/(b/c)/d
x
a+b-(c-d)-e/f
a+b+c-d-(e+f)

i have no idea how to do this. could someone give me an algorithm? then i'll go from there and create my code and post it here for checking...

This post has been edited by futura91: 18 August 2007 - 08:39 PM

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Replies To: Complicated Expressions

#2 PsychoCoder

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• Posts: 19,853
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Re: Complicated Expressions

Posted 18 August 2007 - 08:49 PM

futura91, on 18 Aug, 2007 - 08:35 PM, said:

i have no idea how to do this. could someone give me an algorithm? then i'll go from there and create my code and post it here for checking...

I'm sorry, but I truly doubt, in fact I'm almost 100% positive, no one is just going to hand you an algorithm, thats not what we're here for.

#3 futura91

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• Posts: 12
• Joined: 27-July 07

Re: Complicated Expressions

Posted 18 August 2007 - 09:31 PM

i'm sorry... here, i've got my code. could anyone please check it???

```import java.io.*;
import javax.swing.*;
import java.util.*;

public class MP4{
public static void main(String[] args)
throws IOException{
try{
String fileName = "inMP4.txt";
String str="";
Boolean repeat = true;
StringTokenizer st = new StringTokenizer(str);
String a;
int x=0;
char tD;
char[] b=new char[x];
System.out.println("Output: ");
while(repeat){
if(str==null) {
repeat=false;
break;
}
else{
while(st.hasMoreTokens()){
x = st.countTokens();
a = st.nextToken();
b = a.toCharArray();
for(int i=0;i<x;i++){
tD=str.charAt(i);
if((tD=='(') || (tD==')')){
// this is where i want to delete the parentheses, what method can i use???
}
System.out.println(b);
}
}
}
fr.close();
}
}

catch(NumberFormatException e){
JOptionPane.showMessageDialog(null, "Invalid!", "ERROR MESSAGE", JOptionPane.ERROR_MESSAGE);
}
}
}
```

This post has been edited by futura91: 18 August 2007 - 09:34 PM

#4 futura91

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• Posts: 12
• Joined: 27-July 07

Re: Complicated Expressions

Posted 19 August 2007 - 07:03 PM

i've made revisions to my previous code. but the problem is i can only delete the first parenthesis in a line. how can i make my program delete all the parentheses in every line?

```import java.io.*;
import javax.swing.*;
import java.util.*;

public class MP4Dizon{
public static void main(String[] args)
throws IOException{
try{
String fileName = "d:\\inMP4.txt";
String str="";
Boolean repeat = true;
StringTokenizer st;
String a;
int x=0;
char tD;
System.out.println("Output: ");
StringBuffer bufnew;
while(repeat){
if(str==null) {
repeat=false;
break;
}
else{
st = new StringTokenizer(str);
while(st.hasMoreTokens()){
x = st.countTokens();
a = st.nextToken();
bufnew = new StringBuffer(a);
for(int i=0;i<x;i++){
tD=str.charAt(i);
if((tD=='(') || (tD==')')){
bufnew.deleteCharAt(i);
}
System.out.println(bufnew);
}
}
}
}
fr.close();
}

catch(NumberFormatException e){
JOptionPane.showMessageDialog(null, "Invalid!", "ERROR MESSAGE", JOptionPane.ERROR_MESSAGE);
}
}
}
```