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We are given an RPL (Reverse Polish Notation) expression. We need to evaluate it.
Steps:
Split the input string into tokens (assuming tokens are separated by spaces).
Use a stack to process the tokens.
For each token:
If the token is a number, push it onto the stack.
If the token is an operator (like '+', '-', '*', '/'), pop the top two numbers from the stack.
The first pop is the right operand, the second is the left operand.
Apply the operator: left operator right.
Push the result back onto the stack.
After processing all tokens, the stack should have exactly one element which is the result.
Note: We assume the expression is valid.
Let's write the code accordingly.
To evaluate an RPL (Reverse Polish Notation) expression, we use a stack to process tokens (numbers and operators) from left to right. Numbers are pushed onto the stack, and operators pop the top two numbers, apply the operation, and push the result back. The final result is the only number left on the stack.
Approach
Token Processing: Split the input string into individual tokens (numbers and operators).
Stack Operations:
For each token:
If it's a number, push it onto the stack.
If it's an operator, pop the top two numbers (right operand first, then left operand), compute the result, and push it back.
Result Extraction: After processing all tokens, the stack's top element is the result.
Solution Code
def eval_rpl(tokens):
stack = []
for token in tokens.split():
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)
elif token == '/':
stack.append(a / b)
else:
stack.append(float(token))
return stack.pop()
# Example usage:
# tokens = "3 4 + 2 *"
# print(eval_rpl(tokens)) # Output: 14.0
Explanation
Token Splitting: The input string is split into tokens using split(), which handles spaces between tokens.
Stack Handling:
Numbers: Converted to floats and pushed onto the stack.
Operators: The top two numbers are popped. The operator is applied (e.g., a - b for subtraction), and the result is pushed back.
Final Result: The last remaining number on the stack is returned as the result.
This approach efficiently handles RPL expressions by leveraging stack operations to process each token in sequence, ensuring correct order of operations without parentheses. The algorithm runs in O(n) time, where n is the number of tokens.
RPL（Real-time Program Language）是一种用于实时控制系统的编程语言，主要用于开发实时操作系统和实时控制程序。RPL 语言的特点是语法简洁、执行速度快、易于理解和调试，并且支持多任务、中断处理、数据通信等实时系统所需的功能。
RPL 语言的主要应用领域包括：
实时控制系统：如工业自动化、机器人控制、航空航天等领域的实时控制系统。
实时操作系统：如嵌入式实时操作系统、实时Linux等。
数据采集与处理：如传感器数据采集、信号处理、图像处理等。
测试与测量：如电子测量、物理实验、医疗设备等。
调试与维护：如设备调试、故障诊断、系统维护等。
RPL 语言的学习和开发需要一定的编程基础和实时系统知识，同时还需要熟悉相关硬件和软件环境。对于初学者，建议先学习C/C++、Python等通用编程语言，然后再学习RPL 语言。在实际开发中，可以结合具体的工程需求，选择合适的RPL 语言工具和开发环境。
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发表于 2025-11-10 04:57:38