Inverse Polish expression evaluation
topic
According to the reverse Polish notation, find the value of the expression.
Valid operators include +,-, *, /. Each operand can be an integer or another inverse Polish expression.
Note:
integer division only retains the integer part.
Given an inverse Polish expression is always valid. In other words, the expression always results in a valid value and there is no divisor of 0.
Example 1:
Input: [“2”, “1”, “+”, “3”, “*”]
Output: 9
Explanation: ((2 + 1) * 3) = 9
Example 2:
Input: [“4”, “13”, “5”, “/”, “+”]
Output: 6
Explanation: (4 + (13/5)) = 6
Example 3:
Input: [“10”, “6”, “9”, “3”, “+”, “-11”, “ ", “/”, “ ”, “17”, “+”, “5”, "+"]
Output: 22
Explanation:
((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22
Run the code
class Solution {
public:
int evalRPN(vector<string>& tokens) {
stack<int> temp;
for(int i=0;i<tokens.size();i++)
{
if(tokens[i].size()==1&&(tokens[i][0]=='+'||tokens[i][0]=='-'||tokens[i][0]=='*'||tokens[i][0]=='/'))
{
int temp1=temp.top();
temp.pop();
int temp2=temp.top();
temp.pop();
//cout<<"temp1:"<<temp1<<'.'<<"temp2:"<<temp2<<endl;
if(tokens[i][0]=='+')
temp.push(temp1+temp2);
else if(tokens[i][0]=='-')
temp.push(temp2-temp1);
else if(tokens[i][0]=='*')
temp.push(temp1*temp2);
else
temp.push(temp2/temp1);
}
else
{
temp.push(atoi(tokens[i].c_str()));
}
}
return temp.top();
}
};
operation result
