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
答案：
import java.util.*;
public class Solution {
public int evalRPN(String[] tokens) {
Stack<String> stack = new Stack<String>();
for(String s : tokens) {
if(s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/")) {
int second = Integer.parseInt(stack.pop());
int first = Integer.parseInt(stack.pop());
if(s.equals("+")) {
stack.push(String.valueOf(first+second));
} else if(s.equals("-")) {
stack.push(String.valueOf(first-second));
} else if(s.equals("*")) {
stack.push(String.valueOf(first*second));
} else if(s.equals("/")) {
stack.push(String.valueOf(first/second));
}
} else {
stack.push(s);
}
}
return Integer.parseInt(stack.pop());
}
}
