其实这只是一个栈操作。
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
Note:
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Division between two integers should truncate toward zero.
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The given RPN expression is always valid. That means the expression would always evaluate to a result and there won’t be any divide by zero operation.
Example 1:
Input: ["2", "1", "+", "3", ""] *Output: 9 Explanation: ((2 + 1) * 3) = 9
Example 2:
Input: ["4", "13", "5", "/", "+"] Output: 6 Explanation: (4 + (13 / 5)) = 6
Example 3:
Input: ["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
link:{sourcedir}/_0150_EvaluateReversePolishNotation.java[role=include]