50 lines
1.3 KiB
Python
50 lines
1.3 KiB
Python
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from typing import (
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List,
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)
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from collections import deque
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class Solution:
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"""
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@param expression: A string array
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@return: The Reverse Polish notation of this expression
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"""
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def convert_to_r_p_n(self, expression: List[str]) -> List[str]:
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op_priority = {
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'/': 1 << 4,
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'*': 1 << 4,
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'+': 1 << 2,
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'-': 1 << 2,
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'(': 1 << 0
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}
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op_stack = deque()
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result = []
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for token in expression:
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if token.isdigit():
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result.append(token)
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elif token == '(':
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op_stack.append(token)
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elif token == ')':
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while len(op_stack) > 0 and op_stack[-1] != '(':
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result.append(op_stack.pop())
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op_stack.pop()
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else:
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# For any other operator, keep popping and appending to results as long as there
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# are higher priority operators in the stack
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while len(op_stack) > 0 and op_priority[op_stack[-1]] >= op_priority[token]:
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result.append(op_stack.pop())
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op_stack.append(token)
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# Pop and append the remaining operators in the stack
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while len(op_stack) > 0:
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result.append(op_stack.pop())
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return result
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