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Deepali-SrivastavaDeepali-Srivastava
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Infix to postfix
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3 files changed

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‎stack/postfix/Demo.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package postfix;
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import java.util.Scanner;
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public class Demo
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{
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public static void main(String[] args)
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{
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String infix;
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Scanner scan = new Scanner(System.in);
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System.out.print("Enter infix expression : ");
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infix = scan.nextLine();
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String postfix = infixToPostfix(infix);
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System.out.println("Postfix expression is : " + postfix);
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System.out.println("Value of expression : " + evaluatePostfix(postfix));
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scan.close();
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}
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public static String infixToPostfix(String infix)
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{
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String postfix = new String();
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StackChar st = new StackChar(20);
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char next,symbol;
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for(int i=0; i<infix.length(); i++)
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{
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symbol=infix.charAt(i);
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if(symbol==' ' || symbol=='\t') /*ignore blanks and tabs*/
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continue;
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switch(symbol)
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{
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case '(':
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st.push(symbol);
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break;
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case ')':
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while((next=st.pop())!='(')
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postfix = postfix + next;
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break;
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case '+':
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case '-':
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case '*':
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case '/':
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case '%':
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case '^':
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while( !st.isEmpty() && precedence(st.peek())>= precedence(symbol) )
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postfix = postfix + st.pop();
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st.push(symbol);
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break;
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default: /*operand*/
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postfix = postfix + symbol;
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}
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}
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while(!st.isEmpty())
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postfix = postfix + st.pop();
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return postfix;
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}
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public static int precedence(char symbol)
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{
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switch(symbol)
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{
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case '(':
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return 0;
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case '+':
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case '-':
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return 1;
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case '*':
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case '/':
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case '%':
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return 2;
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case '^':
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return 3;
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default :
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return 0;
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}
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}
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public static int evaluatePostfix(String postfix)
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{
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StackInt st = new StackInt(20);
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int x,y;
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for(int i=0; i<postfix.length(); i++)
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{
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if(Character.isDigit(postfix.charAt(i)))
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st.push(Character.getNumericValue(postfix.charAt(i)));
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else
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{
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x=st.pop();
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y=st.pop();
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switch(postfix.charAt(i))
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{
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case '+':
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st.push(y+x); break;
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case '-':
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st.push(y-x); break;
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case '*':
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st.push(y*x); break;
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case '/':
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st.push(y/x); break;
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case '%':
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st.push(y%x); break;
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case '^':
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st.push(power(y,x));
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}
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}
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}
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return st.pop();
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}
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public static int power(int b,int a)
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{
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int i,x=1;
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for(i=1; i<=a; i++)
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x=x*b;
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return x;
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}
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}
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‎stack/postfix/StackChar.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package postfix;
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import java.util.EmptyStackException;
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public class StackChar
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{
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private char[] stackArray;
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private int top;
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public StackChar()
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{
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stackArray = new char[10];
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top = -1;
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}
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public StackChar(int maxSize)
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{
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stackArray = new char[maxSize];
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top=-1;
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}
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public int size()
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{
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return top+1;
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}
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public boolean isEmpty()
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{
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return (top==-1);
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}
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public boolean isFull()
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{
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return (top==stackArray.length-1);
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}
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public void push(char x)
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{
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if(isFull())
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{
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System.out.println("Stack Overflow\n");
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return;
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}
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top=top+1;
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stackArray[top]=x;
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}
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public char pop()
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{
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char x;
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if(isEmpty())
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{
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System.out.println("Stack Underflow\n");
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throw new EmptyStackException();
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}
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x=stackArray[top];
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top=top-1;
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return x;
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}
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public char peek()
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{
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if(isEmpty())
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{
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System.out.println("Stack Underflow\n");
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throw new EmptyStackException();
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}
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return stackArray[top];
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}
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public void display()
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{
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int i;
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System.out.println("top= " + top);
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if(isEmpty())
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{
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System.out.println("Stack is empty");
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return;
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}
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System.out.println("Stack is : ");
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for(i=top; i>=0; i--)
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System.out.println(stackArray[i] + " ");
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System.out.println();
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}
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}

‎stack/postfix/StackInt.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package postfix;
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import java.util.EmptyStackException;
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public class StackInt
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{
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private int[] stackArray;
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private int top;
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public StackInt()
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{
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stackArray = new int[10];
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top = -1;
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}
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public StackInt(int maxSize)
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{
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stackArray = new int[maxSize];
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top=-1;
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}
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public int size()
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{
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return top+1;
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}
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public boolean isEmpty()
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{
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return (top==-1);
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}
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public boolean isFull()
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{
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return (top==stackArray.length-1);
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}
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public void push(int x)
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{
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if(isFull())
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{
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System.out.println("Stack Overflow\n");
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return;
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}
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top=top+1;
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stackArray[top]=x;
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}
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public int pop()
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{
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int x;
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if(isEmpty())
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{
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System.out.println("Stack Underflow\n");
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throw new EmptyStackException();
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}
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x=stackArray[top];
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top=top-1;
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return x;
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}
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public int peek()
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{
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if(isEmpty())
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{
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System.out.println("Stack Underflow\n");
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throw new EmptyStackException();
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}
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return stackArray[top];
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}
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public void display()
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{
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int i;
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System.out.println("top= " + top);
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if(isEmpty())
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{
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System.out.println("Stack is empty");
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return;
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}
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System.out.println("Stack is : ");
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for(i=top; i>=0; i--)
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System.out.println(stackArray[i] + " ");
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System.out.println();
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}
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}

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