passes 10/21 test cases using stack method with two lists

NeetCodeRoadmap/Stack/150_Evaluate_Reverse_Polish_Notation.py

@@ -0,0 +1,56 @@
+import math
+class Solution(object):
+    def evalRPN(self, tokens):
+        """
+        :type tokens: List[str]
+        :rtype: int
+        """
+        valid_tokens = {
+            '+': lambda x, y: x + y,
+            '-': lambda x, y: x - y,
+            '*': lambda x, y: x * y,
+            '/': lambda x, y: x / y,
+        }
+        tmp = []
+
+        # while len(tokens) != 1:
+        blanks = 0
+        count = 0
+        for x in range(len(tokens)):
+            # print(tokens[x])
+            if tokens[x] in valid_tokens:
+                operator = valid_tokens[tokens[x]]
+                if len(tmp) > 1 and count == 0:
+                    a = tmp.pop()
+                    b = tmp.pop()
+                    tokens.append(math.floor(operator(b, a)))
+                    # print(tmp)
+                    # print(tokens)
+                    tokens[x] = None
+                    count += 1
+                else:
+                    a = tmp.pop()
+                    b = tokens.pop()
+                    tokens.append(math.ceil(operator(a, b)))
+                    tokens[x] = None
+            else:
+                tmp.append(int(tokens[x]))
+                tokens[x] = None
+            # print(tokens)
+            # print(tmp)
+        for y in tokens:
+            if y is None:
+                blanks += 1
+                # print(blanks)
+        tokens = tokens[blanks:]
+        if tokens[0] < 0:
+            tokens[0] *= -1
+        return int(tokens[0])
+
+obj = Solution()
+# print(obj.evalRPN(["2","1","+","3","*"])) # 9
+# print(obj.evalRPN(["4","13","5","/","+"])) # 6
+# print(obj.evalRPN(["10","6","9","3","+","-11","*","/","*","17","+","5","+"])) # 22
+# print(obj.evalRPN(["0","3","/"])) # 0
+print(obj.evalRPN(["3","11","+","5","-"])) # 9
+print(obj.evalRPN(["3","-4","+"])) # -1