Evaluate reverse polish notation (#171)

* Solution of Evaluate Reverse Polish Notation

* Update evaluate_reverse_polish_notation.java

* update readme.md

Author: MoulinaPradhan

Java/evaluate_reverse_polish_notation.java

@@ -0,0 +1,30 @@
+
+
+class Solution {
+    public int evalRPN(String[] tokens) {
+        Stack<Integer> st = new Stack<>();
+        int a,b;
+        for(String s: tokens){
+            if(s.equals("+")){
+                st.add(st.pop()+st.pop());
+            }
+            else if(s.equals("*")){
+                st.add(st.pop() * st.pop());
+            }
+            else if(s.equals("/")){
+                b=st.pop();
+                a = st.pop();
+                st.add(a/b);
+            }
+            else if(s.equals("-")){
+                b = st.pop();
+                a = st.pop();
+                st.add(a-b);
+            }
+            else{
+                st.add(Integer.parseInt(s));
+            }
+        }
+        return st.pop();
+    }
+}

README.md

@@ -198,7 +198,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | ---- | ------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------- | ------ | ------ | ---------- | ---------------------- | ---- |
 | 020  | [Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)                                               | [Python](./Python/20_ValidParentheses.py)                   | _O(n)_ | _O(n)_ | Easy       | Stack                  |      |
 | 084  | [Largest Rectangle in Histogram](https://leetcode.com/problems/largest-rectangle-in-histogram/)                     | [C++](./C++/Largest-Rectangle-in-Histogram.cpp)             | _O(n)_ | _O(n)_ | Hard       | Stack                  |
-| 150  | [Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/)                 | [Python](./Python/150.EvaluateReversePolishNotation.py)     | _O(n)_ | _O(1)_ | Medium     | Stack                  |      |
+| 150  | [Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/)                 | [Python](./Python/150.EvaluateReversePolishNotation.py) <br> [Java](./Java/evaluate_reverse_polish_notation.java)     | _O(n)_ | _O(1)_ | Medium     | Stack                  |      |
 | 1047 | [Remove All Adjacent Duplicates In String](https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string/) | [C++](./C++/remove-all-adjacent-duplicates-in-string.cpp)   | _O(n)_ | _O(n)_ | Easy       | Stack                  |      |
 | 682  | [Baseball Game](https://leetcode.com/problems/baseball-game/)                                                       | [C++](./C++/Baseball-Game.cpp)                              | _O(n)_ | _O(n)_ | Easy       | Stack                  |      |
 | 1381 | [Design a Stack With Increment Operation](https://leetcode.com/problems/design-a-stack-with-increment-operation/)   | [Java](./Java/Design-a-Stack-With-Increment-Operation.java) | _O(n)_ | _O(n)_ | Medium     | Stack                  |      |