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150. Evaluate Reverse Polish Notation#

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, and /. Each operand may be an integer or another expression.

Note:

• Division between two integers should truncate toward zero.
• The given RPN expression is always valid. That means the expression would always evaluate to a result, and there will not be any division by zero operation.

Example 1:

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Input: tokens = ["2","1","+","3","*"]
Output: 9
Explanation: ((2 + 1) * 3) = 9

Example 2:

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Input: tokens = ["4","13","5","/","+"]
Output: 6
Explanation: (4 + (13 / 5)) = 6

Example 3:

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Input: tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
Output: 22
Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22

Constraints:

• 1 <= tokens.length <= 10^4
• tokens[i] is either an operator: "+", "-", "*", "/" or an integer in the range [-200, 200].

Reverse Polish Notation (RPN):

Reverse Polish notation is a postfix mathematical notation in which every operator follows all of its operands.

• It is also known as postfix notation.
• It does not need any parentheses as long as each operator has a fixed number of operands.
• The RPN expression (1 + 2) * (3 + 4) can be written as ( ( 1 2 + ) ( 3 4 + ) * ) in RPN.