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Evaluating Prefix expressions in JavaScript

 

Question: Prefix expression evaluation


A string containing the prefix expression is given to you. Evaluate it and print the single integer giving the answer.

Input Description:
You are given a string ‘s’.

Output Description:
Print the evaluated answer of that string.

Sample Input:
+23
Sample Output:
5

Answer: 


Steps to evaluate a prefix expression:

  1. Split the prefix expression based on space (" ") or blank string ("") as per the given input.
  2. Store the split characters in an array and reverse the array.
  3. Create an evaluation array with no elements (blank array).
  4. Iterate through the elements of the characters array.
  5. If the character is a number, simply push the character into the evaluation array.
  6. if the character is an operator (+, -, *, /, %), then pop 2 elements from the evaluation array. Store the first popped number as the left Operand and the second as the right Operand. 
  7. Calculate the result using the operands and current operator. [left operand (operator) right operand]. You may use switch-case or if-else statements to recognize the operator.
  8. After calculating the result push the result into the evaluation array.
  9. After iterating through all the elements of the characters array, the evaluation Array will have only one number, resulting from the evaluation of the prefix expression.
  10. Pop the element and return it as the output.




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