solve problem Evaluate Reverse Polish Notation

Author: P-ppc

README.md

@@ -266,6 +266,7 @@ All solutions will be accepted!
 |19|[Remove Nth Node From End Of List](https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/description/)|[java/py/js](./algorithms/RemoveNthNodeFromEndOfList)|Medium|
 |526|[Beautiful Arrangement](https://leetcode-cn.com/problems/beautiful-arrangement/description/)|[java/py/js](./algorithms/BeautifulArrangement)|Medium|
 |814|[Binary Tree Pruning](https://leetcode-cn.com/problems/binary-tree-pruning/description/)|[java/py/js](./algorithms/BinaryTreePruning)|Medium|
+|150|[Evaluate Reverse Polish Notation](https://leetcode-cn.com/problems/evaluate-reverse-polish-notation/description/)|[java/py/js](./algorithms/EvaluateReversePolishNotation)|Medium|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/EvaluateReversePolishNotation/README.md

@@ -0,0 +1,2 @@
+# Evaluate Reverse Polish Notation
+This problem is easy to solve by stack

algorithms/EvaluateReversePolishNotation/Solution.java

@@ -0,0 +1,28 @@
+class Solution {
+    public int evalRPN(String[] tokens) {
+        LinkedList<String> stack = new LinkedList<String>();
+        String ops = "+-*/";
+        
+        for (String token : tokens) {
+            if (ops.indexOf(token) != -1) {
+                int value2 = Integer.valueOf(stack.pop()),
+                    value1 = Integer.valueOf(stack.pop());
+                String value = null;
+                
+                if (token.equals("+"))
+                    value = String.valueOf(value1 + value2);
+                else if (token.equals("-"))
+                    value = String.valueOf(value1 - value2);
+                else if (token.equals("*"))
+                    value = String.valueOf(value1 * value2);
+                else if (token.equals("/"))
+                    value = String.valueOf(value1 / value2);
+                stack.push(value);
+            } else {
+                stack.push(token);
+            }
+        }
+        
+        return stack.size() > 0 ? Integer.valueOf(stack.getFirst()) : 0;
+    }
+}

algorithms/EvaluateReversePolishNotation/solution.js

@@ -0,0 +1,28 @@
+/**
+ * @param {string[]} tokens
+ * @return {number}
+ */
+var evalRPN = function(tokens) {
+    let stack = []
+    
+    tokens.forEach(token => {
+        if (['+', '-', '*', '/'].indexOf(token) !== -1) {
+            let value2 = parseInt(stack.pop()),
+                value1 = parseInt(stack.pop()),
+                value = 0
+            if (token == '+')
+                value = value1 + value2
+            else if (token == '-')
+                value = value1 - value2
+            else if (token == '*')
+                value = value1 * value2
+            else if (token == '/')
+                value = parseInt(value1 / value2)
+            stack.push(value)
+        } else {
+            stack.push(token)
+        }
+    })
+    
+    return stack.length > 0 ? parseInt(stack[0]) : 0
+};

algorithms/EvaluateReversePolishNotation/solution.py

@@ -0,0 +1,26 @@
+class Solution(object):
+    def evalRPN(self, tokens):
+        """
+        :type tokens: List[str]
+        :rtype: int
+        """
+        stack = []
+        
+        for token in tokens:
+            if token in ['+', '-', '*', '/']:
+                value2 = int(stack.pop())
+                value1 = int(stack.pop())
+                value = 0
+                if token == '+':
+                    value = value1 + value2
+                elif token == '-':
+                    value = value1 - value2
+                elif token == '*':
+                    value = value1 * value2
+                elif token == '/':
+                    value = int(value1 * 1.0 / value2)
+                stack.append(value)
+            else:
+                stack.append(token)
+        
+        return 0 if len(stack) == 0 else int(stack[0])