[Coderbyte] Reverse Polish Notation (Python)

Problem Statement

Reverse Polish Notation: It is a mathematical notation in which operators follow their operands. Watch this video for more detailed explanation.

For example, given 3 4 + 2 * 1 +, the operation would be: (3+4) *2 +1 = 15. Whenever we see a number, we push to stack and if an operator, pop and perform the calculation and push it back to stack.

Example

Example 1

Input: "3 4 + 2 * 1 +"
Output: 15

Example 2

Input: "3 5 + 7 2 – *"
Output: 40

Explanation

1. Create a stack
2. When its a number, append to stack.
3. If it is an operation, pop and evaluate the statement, then pop back in

Code Implementation

def polish_eval(strArr):
    split_arr = strArr.split()
    stack = []

    for i in split_arr:
        if re.match ([\+\-\*\/], i):
            val2 = stack.pop()
            val1 = stack.pop()
						var = str(val1)+i+str(val2)
            stack.append(eval(var))
        else:
            stack.append(int(i))
    return stack[0]