Question
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
Solution
TODO
Code
class Solution {
public int evalRPN(String[] tokens) {
Stack<Integer> stack = new Stack();
for(String token : tokens) {
if(token.equals("+")) {
int v2 = stack.pop();
int v1 = stack.pop();
stack.push(v1+v2);
}
else if (token.equals("-")) {
int v2 = stack.pop();
int v1 = stack.pop();
stack.push(v1-v2);
}
else if (token.equals("*")) {
int v2 = stack.pop();
int v1 = stack.pop();
stack.push(v1*v2);
}
else if (token.equals("/")) {
int v2 = stack.pop();
int v1 = stack.pop();
stack.push(v1/v2);
}
else {
stack.push(Integer.valueOf(token));
}
}
return stack.peek();
}
}
Performance
TODO