add 150 stack

Author: MatNoble

LeetCodeSolutions/150.py

@@ -0,0 +1,40 @@
+#==================================================
+#==>      Title:                                     
+#==>     Author: Zhang zhen                   
+#==>      Email: hustmatnoble.gmail.com
+#==>     GitHub: https://github.com/MatNoble
+#==>       Date: 
+#==================================================
+
+from typing import List
+class Solution:
+    def evalRPN(self, tokens: List[str]) -> int:
+        n = len(tokens)
+        # if n < 3: return False
+        i = res = 0
+        stack = []
+        while i<n:
+            if tokens[i] == '+':
+                tmp = stack.pop()
+                res = stack.pop() + tmp
+            elif tokens[i] == '-':
+                tmp = stack.pop()
+                res = stack.pop() - tmp
+            elif tokens[i] == '*':
+                tmp = stack.pop()
+                res = stack.pop() * tmp
+            elif tokens[i] == '/':
+                tmp = stack.pop()
+                res = int(stack.pop() / tmp)
+            else:
+                res = int(tokens[i])
+            stack.append(res)
+            i += 1
+        return stack[0]
+
+mat = Solution()
+tokens = ["2", "1", "+", "3", "*"]
+# tokens = ["4", "13", "5", "/", "+"]
+# tokens = ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]
+tokens = ["18"]
+mat.evalRPN(tokens)