逆波兰表达式求值

逆波兰表达式求值

150. 逆波兰表达式求值

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> stk;
        int n=tokens.size();
        for(int i=0;i<n;i++){
            if(tokens[i]=="+" || tokens[i]=="-" || tokens[i]=="*" || tokens[i]=="/"){
                int num2 = stk.top();
                stk.pop();
                int num1 = stk.top();
                stk.pop();
                if(tokens[i]=="+"){
                    stk.push(num1+num2);
                }
                if(tokens[i]=="-"){
                    stk.push(num1-num2);
                }
                if(tokens[i]=="*"){
                    stk.push(num1*num2);
                }
                if(tokens[i]=="/"){
                    stk.push(num1/num2);
                }
            }else{  //数字入栈
                stk.push(stoi(tokens[i]));
            }
        }
        return stk.top();
    }
};

func evalRPN(tokens []string) int {
    stk := []int{} // 用切片模拟栈
    n := len(tokens)
    for i := 0; i < n; i++ {
        if tokens[i] == "+" || tokens[i] == "-" || tokens[i] == "*" || tokens[i] == "/" {
            num2 := stk[len(stk)-1]
            stk = stk[:len(stk)-1]
            num1 := stk[len(stk)-1]
            stk = stk[:len(stk)-1]
            if tokens[i] == "+" {
                stk = append(stk, num1+num2)
            }
            if tokens[i] == "-" {
                stk = append(stk, num1-num2)
            }
            if tokens[i] == "*" {
                stk = append(stk, num1*num2)
            }
            if tokens[i] == "/" {
                stk = append(stk, num1/num2)
            }
        } else { // 数字入栈
            num, _ := strconv.Atoi(tokens[i])
            stk = append(stk, num)
        }
    }
    return stk[len(stk)-1]
}