feat: add eval reverse polish notation

Author: adhocore

evalrpn.py

@@ -0,0 +1,29 @@
+class Solution(object):
+    def evalRPN(self, tokens):
+        stak = []
+        for i in range(len(tokens)):
+            if not tokens[i] in "+-*/":
+                stak.append(int(tokens[i]))
+                continue
+            a, b = stak.pop(), stak.pop()
+            if tokens[i] == "+":
+                stak.append(b + a)
+            elif tokens[i] == "-":
+                stak.append(b - a)
+            elif tokens[i] == "*":
+                stak.append(b * a)
+            elif tokens[i] == "/":
+                stak.append(int(b / a))
+        return stak.pop()
+
+
+if __name__ == "__main__":
+    s = Solution()
+    print(s.evalRPN(["2", "1", "+", "3", "*"]))
+    # => 9 => (2+1)*3
+    print(
+        s.evalRPN(["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"])
+    )
+    # => 22
+    print(s.evalRPN(["4", "-2", "/", "2", "-3", "-", "-"]))
+    # => -7