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  • 150. Evaluate Reverse Polish Notation (Stack)

    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
    
    class Solution {
    public:
        int evalRPN(vector< string > &tokens) {
            stack< int > operandStack;
            int operand1;
            int operand2;
            for(int i = 0; i < tokens.size(); i++){
                if(tokens[i]=="+"){
                    operand1 = operandStack.top();
                    operandStack.pop();
                    operand2 = operandStack.top();
                    operandStack.pop();
                    operand2 += operand1;
                    operandStack.push(operand2);
                }
                else if(tokens[i]=="-"){
                    operand1 = operandStack.top();
                    operandStack.pop();
                    operand2 = operandStack.top();
                    operandStack.pop();
                    operand2 -= operand1;
                    operandStack.push(operand2);
                }
                else if(tokens[i]=="*"){
                    operand1 = operandStack.top();
                    operandStack.pop();
                    operand2 = operandStack.top();
                    operandStack.pop();
                    operand2 *= operand1;
                    operandStack.push(operand2);
                }
                else if(tokens[i]=="/"){
                    operand1 = operandStack.top();
                    operandStack.pop();
                    operand2 = operandStack.top();
                    operandStack.pop();
                    operand2 /= operand1;
                    operandStack.push(operand2);
                }
                else{
                    operand1 = atoi(tokens[i].c_str());
                    operandStack.push(operand1);
                }
            }
            return operandStack.top();
        }
    };
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  • 原文地址:https://www.cnblogs.com/qionglouyuyu/p/4854191.html
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