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Evaluator.java
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Evaluator.java
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import java.util.*;
interface IStack {
/*** Removes the element at the top of stack and returnsthat element.
* @return top of stack element, or through exception if empty
*/
public Object pop();
/*** Get the element at the top of stack without removing it from stack.
* @return top of stack element, or through exception if empty
*/
public Object peek();
/*** Pushes an item onto the top of this stack.
* @param object to insert*
*/
public void push(Object element);
/*** Tests if this stack is empty
* @return true if stack empty
*/
public boolean isEmpty();
public int size();
}
class MyStack implements IStack {
class Node {
Object data;
Node next;
}
Node head = null;
static int length = 0;
public void push(Object element) {
Node temp = new Node();
temp.data = element;
if (head == null) {
temp.next = null;
head = temp;
} else {
temp.next = head;
head = temp;
}
length++;
}
public Object pop() {
if (head == null)
return 0;
Object curr = head.data;
head = head.next;
length--;
return curr;
}
public boolean isEmpty() {
if (head == null)
return true;
return false;
}
public Object peek() {
if (head == null)
return 0;
return head.data;
}
public int size() {
return length;
}
}
interface IExpressionEvaluator {
/**
* Takes a symbolic/numeric infix expression as input and converts it to
* postfix notation. There is no assumption on spaces between terms or the
* length of the term (e.g., two digits symbolic or numeric term)
*
* @param expression infix expression
* @return postfix expression
*/
public String infixToPostfix(String expression);
/**
* Evaluate a postfix numeric expression, with a single space separator
* @param expression postfix expression
* @return the expression evaluated value
*/
public int evaluate(String expression);
}
public class Evaluator implements IExpressionEvaluator{
static int a,b,c;
int operator(char op) //returns the equivalent priority of this operator
{
if(op=='+' || op=='-') return 1;
else if(op=='*' || op=='/') return 2;
else if(op=='^') return 3;
else return 0;
}
public String infixToPostfix(String expression){
MyStack stack = new MyStack();
String postfix = "";
int count1 = 0;
int count2 = 0;
for(int i=0;i<expression.length();i++){
char var = expression.charAt(i);
if(var =='a' || var =='b' || var =='c'){
postfix += var;
count1++;
}
else if( var =='+' || var =='-' || var =='*' || var =='/' || var =='^'){
count2++;
while( !stack.isEmpty() && operator(var) <= operator(String.valueOf(stack.peek()).charAt(0)) ){
postfix += String.valueOf(stack.pop());
}
stack.push(var);
}
else if(var =='(')
stack.push(var);
else if(var ==')'){
while(!(String.valueOf(stack.peek()).equals("("))){
postfix += String.valueOf(stack.pop());
}
stack.pop();
}
else {
System.out.println("Error");
break;
}
}
if(count1<count2) {
System.out.println("Error");
return "";
}
while(!stack.isEmpty())
postfix += String.valueOf(stack.pop());
return postfix;
}
/**
* takes the evaluator stack and char operator
* and forms the operation on on the stack elements
* to evaluate the postfix expression
* @param stack
* @param op
*/
void solve(MyStack stack,char op){
int x=0, y=0; //first, second operands
String pop2 = String.valueOf(stack.pop());
String pop1 = String.valueOf(stack.pop());
//convert each letter by it's specific number if letter exist otherwise take the number
if(pop1.equals("a"))
x = a;
else if(pop1.equals("b"))
x = b;
else if(pop1.equals("c"))
x = c;
else
x = Integer.parseInt(pop1);
if(pop2.equals("a"))
y = a;
else if(pop2.equals("b"))
y = b;
else if(pop2.equals("c"))
y = c;
else
y = Integer.parseInt(pop2);
String res = new String();
switch(op){
case '+':
res = String.valueOf(x+y);
break;
case '-':
res = String.valueOf(x-y);
break;
case '*':
res = String.valueOf(x*y);
break;
case '/':
res = String.valueOf(x/y);
break;
case '^':
res = String.valueOf((int)Math.pow(x,y));
break;
}
stack.push(res);
}
public int evaluate(String expression){
MyStack stack = new MyStack();
for(int i=0;i<expression.length();i++){
char op = expression.charAt(i);
if(op=='a' || op=='b' || op=='c')
stack.push(op);
else if(op=='+' || op=='*' || op=='/' || op=='^'){
solve(stack, op);
}
else if(op=='-'){
if(stack.size()==1){
String pop = String.valueOf(stack.pop());
int oper = 0;
if(pop.equals("a"))
oper = a;
else if(pop.equals("b"))
oper = b;
else if(pop.equals("c"))
oper = c;
else
oper = Integer.parseInt(pop);
String negative = String.valueOf(-oper);
stack.push(negative);
}
else{
solve(stack, op);
}
}
}
if(stack.size()>=2) {
System.out.println("Error");
return 0;
}
else
return Integer.parseInt(String.valueOf(stack.pop()));
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
try{
String infix = input.nextLine();
String sin1 = input.nextLine();
String sin2 = input.nextLine();
String sin3 = input.nextLine();
a = Integer.parseInt(sin1.replaceAll("a=", ""));
b = Integer.parseInt(sin2.replaceAll("b=", ""));
c = Integer.parseInt(sin3.replaceAll("c=", ""));
int count1=0, count2=0;
for(int i=0;i<infix.length()-1;i++){
if(infix.charAt(i)=='(' && infix.charAt(i+1)==')') {
System.out.println("Error");
break;
}
}
for(int i=0;i<infix.length();i++){
if(infix.charAt(i)=='(')
count1++;
else if(infix.charAt(i)==')')
count2++;
}
if(count1!=count2)
{
System.out.println("Error");
return;
}
infix = infix.replaceAll("--", "+");
if(infix.charAt(0)=='+') infix = infix.substring(1);
infix = infix.replace("/+", "/");
infix = infix.replace("-+", "-");
infix = infix.replace("*+", "*");
infix = infix.replace("^+", "^");
infix = infix.replace("++", "+");
if(infix.length()==1 && (infix.charAt(0)=='a' ||infix.charAt(0)=='b' || infix.charAt(0)=='c' ))
{
System.out.println(infix.charAt(0));
int result=0;
if(infix.charAt(0) =='a') result = a;
else if(infix.charAt(0) =='b') result = b;
else result = c;
System.out.println(result);
return;
}
for(int i=0;i<infix.length()-1;i++){
if( infix.charAt(i)=='/' && infix.charAt(i+1)=='/' || infix.charAt(i)=='*' && infix.charAt(i+1)=='*' || infix.charAt(i)=='^' && infix.charAt(i+1)=='^' )
{
System.out.println("Error");
break;
}
}
if(infix.charAt(0)=='*' || infix.charAt(0)=='/' || infix.charAt(0)=='^')
{
System.out.println("Error");
return;
}
if((infix.charAt(infix.length()-1) > 41 && infix.charAt(infix.length()-1) < 48) || infix.charAt(infix.length()-1)=='^')
{
System.out.println("Error");
return;
}
Evaluator sol = new Evaluator();
String postfix = sol.infixToPostfix(infix);
System.out.println(postfix);
int result = sol.evaluate(postfix);
System.out.println(result);
}
catch(Exception e){
System.out.println("Error");
}
}
}