Input: [“3”, “1”, “+”, “5”, “*”]

Output: 9

Explanation: ((3 + 1) * 5) = 20

### Algorithm:

The key thing to realize in this to use stack as a data structure for the solution. Also, in most of the mathematical operations stack is used.

- Push operands to stack until you encounter an operator
- When you encounter an operator, pop two operands from stack
- Calculate operands using given operator and push the result to the stack