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Infix to Prefix Conversion:-
In this page we will learn the infix to prefix conversion in Java .
Suppose there are two operands A and B and an operator (op) , the infix conversion implies that op will be placed in between a and b i.e a op b. When the operator is placed after both operands i.e ab op , it is called postfix notation. And when the operator is placed before the operands i.e op ab , the expression in prefix notation.
let us see how to do this in java :-


ALGORITHM:
Reverse the given infix expression.
Do Infix to postfix conversion and get the result.
Reverse the result to get the final expression. (prefix expression) .
Java code :
Run
import java.util.Stack; public class Main { static int precedence(char c){ switch (c){ case '+': case '-': return 1; case '*': case '/': return 2; case '^': return 3; } return 1; } static StringBuilder infixToPreFix(String expression){ StringBuilder result = new StringBuilder(); StringBuilder input = new StringBuilder(expression); input.reverse(); Stack<Character> stack = new Stack<Character>(); char [] charsExp = new String(input).toCharArray(); for (int i = 0; i < charsExp.length; i++) { if (charsExp[i] == '(') { charsExp[i] = ')'; i++; } else if (charsExp[i] == ')') { charsExp[i] = '('; i++; } } for (int i = 0; i < charsExp.length ; i++) { char c = charsExp[i]; if(precedence(c)>0){ while(stack.isEmpty()==false && precedence(stack.peek())>=precedence(c)){ result.append(stack.pop()); } stack.push(c); }else if(c==')'){ char x = stack.pop(); while(x!='('){ result.append(x); x = stack.pop(); } }else if(c=='('){ stack.push(c); }else{ //character is neither operator nor “(“ result.append(c); } } for (int i = 0; i <=stack.size() ; i++) { result.append(stack.pop()); } return result.reverse(); } public static void main(String[] args) { String exp = "A+B*(C^D-E)"; System.out.println("Infix Expression: "+ exp); System.out.println("Prefix Expression:" + infixToPreFix(exp)); } }
Output:
Infix Expression: A+B*(C^D-E) Prefix Expression: +A*B-^CDE
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