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150. Evaluate Reverse Polish Notation QuestionEditorial Solution
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
Some examples:
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9 ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
stack只存数字，遇到operator则pop两个数字并进行计算，然后将结果存stack。最后stack的第一个元素就是答案。
注意 - 与 / 的差别， 先pop的值在算符右边。
public int EvalRPN(string[] tokens) { Stack<int> stack = new Stack<int>(); for(int i = 0;i< tokens.Count();i++) { if(tokens[i] == "+") { stack.Push(stack.Pop() + stack.Pop()); } else if(tokens[i] == "-") { stack.Push(-1*stack.Pop() + stack.Pop()); } else if(tokens[i] == "*") { stack.Push(stack.Pop() * stack.Pop()); } else if(tokens[i] == "/") { int a = stack.Pop(); int b = stack.Pop(); stack.Push(b / a); } else { stack.Push(Int32.Parse(tokens[i])); } } return stack.Peek(); }
150. Evaluate Reverse Polish Notation QuestionEditorial Solution
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