[stack]Evaluate Reverse Polish Notation

Total Accepted: 55722 Total Submissions: 249668 Difficulty: Medium

 

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

 (M) Basic Calculator (H) Expression Add Operators

 

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        int tokens_size = tokens.size();
        int i=0,k=0;
        long long int num1 =0,num2=0;
        while(i<tokens_size){
            if(tokens[i]=="+" || tokens[i]=="-" || tokens[i]=="*" ||tokens[i]=="/"){
                num2 = stoi(tokens[--k]);
                num1 = stoi(tokens[--k]);
                switch(tokens[i][0]){
                    case '+': num1+=num2;break;
                    case '-': num1-=num2;break;
                    case '*': num1*=num2;break;
                    case '/': num1/=num2;break;
                }
                tokens[k++] = to_string(num1);
                i++;
            }else{
                tokens[k++]=tokens[i++];
            }
        }
        return stoi(tokens[0]);
    }
};

Next challenges: (H) Maximal Rectangle (M) Binary Tree Preorder Traversal (M) Binary Search Tree Iterator