Leetcode Evaluate Reverse Polish Notation

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

此题是求解后缀表达式，题目比较简单，开一个数据stack即可，此题的改进版本是引入括号，此时要开一个数据stack和运算符stack

bool isOperator(string& op){

    if(op == "+" ||  op == "-" || op == "*" || op == "/") return true;

    else return false;

}

int calc(int a, int b, char op){

    switch(op){

        case '+':return a+b;

        case '-':return a-b;

        case '*':return a*b;

        case '/':return a/b;

    }

}

int evalRPN(vector<string> &tokens){

    stack<int> num;

    for(int i =  ; i < tokens.size(); ++ i){

        if(!isOperator(tokens[i])){

            num.push(atoi(tokens[i].c_str()));

        }else{

            int num2 = num.top(); num.pop();

            int num1 = num.top(); num.pop();

            char op = tokens[i][];

            num.push(calc(num1,num2,op));

        }

    }

    return num.top();

}

巴特西

Leetcode Evaluate Reverse Polish Notation

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