Add solution 150.

Author: javadev

src/Algorithms/0150.evaluate-reverse-polish-notation/evaluate-reverse-polish-notation.php

@@ -0,0 +1,42 @@
+class Solution {
+
+    /**
+     * @param String[] $tokens
+     * @return Integer
+     */
+    function evalRPN($tokens) {
+        $stack = [];
+        $conVal=0;
+        $res=0;
+        
+        if(count($tokens)<2)return intval($tokens[0]);
+        foreach($tokens as $s){
+            if(($s == "+") || ($s == "-") || ($s == "*") || ($s == "/")){
+                switch($s){
+                    case "+" : $res=array_pop($stack)+array_pop($stack);
+                               array_push($stack, $res);
+                               break;
+                    case "-" : $x = array_pop($stack);
+                               $y = array_pop($stack);
+                               $res=$y-$x;
+                               array_push($stack, $res);
+                               break;
+                    case "*" : $res=array_pop($stack)*array_pop($stack);
+                               array_push($stack, $res);
+                               break;
+                    case "/" : $a = array_pop($stack);
+                               $b = array_pop($stack);
+                               if($b==0)$res=0;
+                               else $res=intval($b/$a);
+                               array_push($stack, $res);
+                               break;
+                 }
+            }
+          else{
+                $conVal = intval($s);
+                array_push($stack, $conVal);
+            }
+        }
+      return $res;
+    }
+}