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EvalRPN150.java
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EvalRPN150.java
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package Leetcode;
import java.util.Deque;
import java.util.LinkedList;
public class EvalRPN150 {
/*Method: Stack, Time: O(N), Space:O(N)**/
public int evalRPN(String[] tokens) {
Deque<Integer> stack = new LinkedList<Integer>();
int n=tokens.length;
for(int i=0; i<n;i++){
String token = tokens[i];
if(isNumber(token)) {
stack.push(Integer.parseInt(token));
} else {
int num2 = stack.pop();
int num1 = stack.pop();
switch(token) {
case "+":
stack.push(num1 + num2);
break;
case "-":
stack.push(num1-num2);
break;
case "*":
stack.push(num1 * num2);
break;
case "/":
stack.push(num1/ num2);
break;
default:
}
}
}
return stack.pop();
}
private boolean isNumber(String token) {
return !("+".equals(token) || "-".equals(token) || "*".equals(token) || "/".equals(token));
}
}