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Leetcode Evaluate Reverse Polish Notation

2024-07-08 16:51:05   215人阅读

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 = 0 ; 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][0];            num.push(calc(num1,num2,op));        }    }    return num.top();}

 

 


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