Prefix to Infix Conversion

Infix : An expression is called the Infix expression if the operator appears in between the operands in the expression. Simply of the form (operand1 operator operand2).
Example : (A+B) * (C-D)

Prefix : An expression is called the prefix expression if the operator appears in the expression before the operands. Simply of the form (operator operand1 operand2).
Example : *+AB-CD (Infix : (A+B) * (C-D) )

Given a Prefix expression, convert it into a Infix expression.

分析：

Read the Prefix expression in reverse order (from right to left)
If the symbol is an operand, then push it onto the Stack
If the symbol is an operator, then pop two operands from the Stack
Create a string by concatenating the two operands and the operator between them.
string = (operand1 + operator + operand2)
And push the resultant string back to Stack
Repeat the above steps until end of Prefix expression.

 class Solution {

     boolean isOperator(char x) {

         switch (x) {

             case '+':

             case '-':

             case '/':

             case '*':

                 return true;

             default:

                 return false;

         }

     }

     String preToInfix(String pre_exp) {

         Stack<String> stack = new Stack<>();

         int length = pre_exp.length();

         for (int i = length - ; i >= ; i--) {

             if (isOperator(pre_exp.charAt(i))) {

                 String op1 = stack.pop();

                 String op2 = stack.pop();

                 String temp = "(" + op1 + pre_exp.charAt(i) + op2 + ")";

                 stack.push(temp);

             } else {

                 stack.push(pre_exp.charAt(i) + "");

             }

         }

         return stack.peek();

     }

 }

巴特西

Prefix to Infix Conversion

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