We use a stack to store operands. When we encounter an operator, we pop the top two operands, apply the operator, and push the result back onto the stack.

1. Initialize an empty stack.
2. Iterate through each token in the input:
   • If token is an operator:
     • Pop b (the second operand).
     • Pop a (the first operand).
     • Perform the operation a operator b.
     • Push the result back to stack. (For division, use int(a / b) to truncate towards zero).
   • Else (operand):
     • Push the integer value of the token.
3. Return the only element remaining in the stack.

• Time Complexity: O(N).
• Space Complexity: O(N).

def eval_rpn(tokens):
    stack = []
    
    for token in tokens:
        if token in "+-*/":
            b = stack.pop()
            a = stack.pop()
            
            if token == '+':
                stack.append(a + b)
            elif token == '-':
                stack.append(a - b)
            elif token == '*':
                stack.append(a * b)
            else:
                # Truncate towards zero
                stack.append(int(a / b))
        else:
            stack.append(int(token))
            
    return stack[0]