150. Evaluate Reverse Polish Notation
class Solution { public int evalRPN(String[] tokens) { Stack<Integer> stack=new Stack<Integer>(); for(String token:tokens) { if(token.equals("+")||token.equals("-")||token.equals("*")||token.equals("/")) { int n2=stack.pop(); int n1=stack.pop(); if(token.equals("+")) stack.push(n1+n2); else if(token.equals("-")) stack.push(n1-n2); else if(token.equals("*")) stack.push(n1*n2); else stack.push(n1/n2); } else stack.push(Integer.parseInt(token)); } return stack.isEmpty()?0:stack.pop(); } }