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90 lines
2.8 KiB
Java
90 lines
2.8 KiB
Java
// Name: B6-24
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// Date: 1/7/20
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import java.util.*;
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public class Infix
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{
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public static void main(String[] args)
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{
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System.out.println("Infix \t-->\tPostfix\t\t-->\tEvaluate");
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/*build your list of Infix expressions here */
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ArrayList<String> infixExp = new ArrayList<String>();
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infixExp.add("3 - 4 + 5");
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infixExp.add("3 + 4 * 5");
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infixExp.add("3 * 4 + 5");
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infixExp.add("( -5 + 15 ) - 6 / 3");
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infixExp.add("( 3 + 4 ) * ( 5 + 6 )");
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infixExp.add("( 3 * ( 4 + 5 ) - 2 ) / 5");
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infixExp.add("8 + -1 * 2 - 9 / 3");
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infixExp.add("3 * ( 4 * 5 + 6 )");
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infixExp.add("3 * ( 4 * 5 - 6 + 2 )");
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for( String infix : infixExp )
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{
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String pf = infixToPostfix(infix); //get this to work first
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// System.out.println(infix + "\t\t\t" + pf);
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System.out.println(infix + "\t\t\t" + pf + "\t\t\t" + Postfix.eval(pf)); //Postfix must work!
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}
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}
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public static String infixToPostfix(String infix)
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{
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List<String> infixParts = new ArrayList<String>(Arrays.asList(infix.split(" ")));
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/* enter your code here */
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Stack<String> s = new Stack<>();
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String postfix = "";
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for (String str : infixParts) {
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switch(str) {
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case "(":
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s.push(str);
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break;
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case ")":
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while (!s.peek().equals("("))
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postfix += s.pop() + " ";
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s.pop();
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break;
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case "+": case "-": case "/": case "*":
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while(!s.isEmpty() && isLowerOrEqual(str.charAt(0), s.peek().charAt(0)))
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postfix += s.pop() + " ";
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s.push(str);
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break;
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default:
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postfix += str + " ";
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break;
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}
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}
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while (!s.isEmpty())
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postfix += s.pop() + " ";
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return postfix.trim();
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}
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//returns true if c1 has lower or equal precedence than c2
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public static boolean isLowerOrEqual(char c1, char c2)
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{
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String str1 = Character.toString(c1), str2 = Character.toString(c2);
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if (("*/".contains(str2) && "+-".contains(str1)) || ("+-".contains(str2) && "+-".contains(str1)) || ("*/".contains(str2) && "*/".contains(str1)))
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return true;
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else
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return false;
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}
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}
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/********************************************
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Infix --> Postfix --> Evaluate
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3 - 4 + 5 3 4 - 5 + 4
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3 + 4 * 5 3 4 5 * + 23
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3 * 4 + 5 3 4 * 5 + 17
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( -5 + 15 ) - 6 / 3 -5 15 + 6 3 / - 8
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( 3 + 4 ) * ( 5 + 6 ) 3 4 + 5 6 + * 77
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( 3 * ( 4 + 5 ) - 2 ) / 5 3 4 5 + * 2 - 5 / 5
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8 + -1 * 2 - 9 / 3 8 -1 2 * + 9 3 / - 3
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3 * ( 4 * 5 + 6 ) 3 4 5 * 6 + * 78
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3 * ( 4 * 5 - 6 + 2 ) 3 4 5 * 6 - 2 + * 48
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***********************************************/ |