Reverse Polish notation solution (algorithm)

Reverse Polish notation (RPN), also known as Polish postfix notation or simply postfix notation, is a mathematical notation in which operators follow their operands, in contrast to Polish notation (PN), in which operators precede their operands. It does not need any parentheses as long as each operator has a fixed number of operands. In comparison testing of reverse Polish notation with algebraic notation, reverse Polish has been found to lead to faster calculations. Because reverse Polish calculators do not need expressions to be parenthesized, fewer operations need to be entered to perform typical calculations.

for each token in the reversed postfix expression:
  if token is an operator:
    push token onto the operator stack
    pending_operand ← False
  else if token is an operand:
    operand ← token
    if pending_operand is True:
      while the operand stack is not empty:
        operand_1 ← pop from the operand stack
        operator ← pop from the operator stack
        operand ← evaluate operator with operand_1 and operand
    push operand onto the operand stack
    pending_operand ← True
result ← pop from the operand stack

Example

The infix expression ((15 ÷ (7 − (1 + 1))) × 3) − (2 + (1 + 1)) can be written like this in reverse Polish notation:

15 7 1 1 + − ÷ 3 × 2 1 1 + + −

Web service (using spring boot)

Spring Boot contains a comprehensive infrastructure support for developing a micro service (rest-api).

• Simple scalability
• Compatible with Containers
• Minimum configuration
• Lesser production time

API using example

do POST http://[your host]:[port]/calculator-1.0/calculate

Header['Accept'] = application/json

Body:

{
	"variables":{
		"a":"AAAAA",
		"b":-5
	},
	"expression":"sizeof(a)+2*b-abs(3-b)"
}

The expression can contains:

• integer constants
• string constants
• binary operators +,-,*,/
• unary operators sizeof (string) – length of the string argument
• unary operators abs(int) - absolute value of the integer argument

Example response:

{
    "variables": {
        "a": "AAAAA",
        "b": -5
    },
    "expression": "sizeof(a)+2*b-abs(3-b)",
    "result": -13
}

for details please look swagger documenation: http://[your host]:[port]/calculator-1.0/swagger-ui.html

build && deploy

For .war file creation use:

$mvn package

To deploy aplication to tomcat server please move /build/calculator-1.0.war to tomcat webapp directory