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+/*
+Evaluate the value of an arithmetic expression in Reverse Polish Notation.
+
+Valid operators are +, -, *, /. Each operand may be an integer or another expression.
+
+
+
+Input Format
+
+The only argument given is character array A.
+Output Format
+
+Return the value of arithmetic expression formed using reverse Polish Notation.
+For Example
+
+Input 1:
+A = ["2", "1", "+", "3", "*"]
+Output 1:
+9
+Explaination 1:
+starting from backside:
+*: ( )*( )
+3: ()*(3)
++: ( () + () )*(3)
+1: ( () + (1) )*(3)
+2: ( (2) + (1) )*(3)
+((2)+(1))*(3) = 9
+
+Input 2:
+A = ["4", "13", "5", "/", "+"]
+Output 2:
+6
+Explaination 2:
++: ()+()
+/: ()+(() / ())
+5: ()+(() / (5))
+1: ()+((13) / (5))
+4: (4)+((13) / (5))
+(4)+((13) / (5)) = 6
+
+*/
+
+public class Solution {
+public int evalRPN(ArrayList<String> A) {
+if(A.size()== 0)
+return 0;
+Stack<String> stk = new Stack<String>();
+for(String s : A )
+{
+if(s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/"))
+{
+int b = Integer.parseInt(stk.pop());
+int a = Integer.parseInt(stk.pop());
+switch(s)
+{
+case "/" : stk.push( Integer.toString(a/b) );
+break;
+case "*" : stk.push( Integer.toString(b*a) );
+break;
+case "+" : stk.push( Integer.toString(b+a) );
+break;
+case "-" : stk.push( Integer.toString(a-b));
+break;
+}
+}
+else
+{
+stk.push(s);
+}
+}
+return Integer.parseInt(stk.pop());
+}
+}