Create ReversePolishNotation.java

Author: harshithasudhakar

Stacks/Problems/ReversePolishNotation.java

@@ -0,0 +1,32 @@
+class ReversePolishNotation { // Postfix
+    public int evalRPN(String[] tokens) {
+        Stack<Integer> stk = new Stack<>();
+        
+        for(String i : tokens){
+            if(i.equals("+")){
+                int b = stk.pop();
+                int a = stk.pop();
+                stk.push(a+b);
+            }
+            else if(i.equals("-")){
+                int b = stk.pop();
+                int a = stk.pop();
+                stk.push(a-b);
+            }
+            else if(i.equals("*")){
+                int b = stk.pop();
+                int a = stk.pop();
+                stk.push(a*b);
+            }
+            else if(i.equals("/")){
+                int b = stk.pop();
+                int a = stk.pop();
+                stk.push(a/b);
+            }
+            else{
+                stk.push(Integer.parseInt(i));
+            }
+        }
+        return stk.pop();
+    }
+}